REFERENCE MANUAL FOR PRACTICAL PERIPHERALS MODEMS Practical Peripherals, Inc. Life Support Policy Practical Peripherals' products are not intended for use in life critical situations or as critical components in life support devices or systems. Life support devices or systems are defined as devices which are intended for surgical implant into the body, or for support or sustaining life, and whose failure to perform, when used in accordance with the instructions provided by the manufacturer, might result in injury to the user. Practical Peripherals, Inc., reserves the right to make improvements in the hardware, firmware, and software described in this manual at any time and without notice. The use of trademarks or other designations in this publication is for reference purposes only. PRACTICAL PERIPHERALS, INC. 375 Conejo Ridge Avenue Thousand Oaks, CA 91361 (805) 496-7707 P/NL1125342 Rev. 1.000 TABLE OF CONTENTS NOTE: The page numbers listed in the Table of Contents are for general reference only. They may change according to the program used to display/print the document. 1 INTRODUCTION 1-1 Typographical Conventions 1-1 2 S-REGISTERS 2-1 S0 Ring to Answer On 2-1 S1 Ring Count 2-1 S2 Escape Code Character 2-1 S3 Carriage Return Character 2-1 S4 Linefeed Character 2-1 S5 Backspace Character 2-2 S6 Wait Time before Blind Dialing 2-2 S7 Wait for Carrier after Dial 2-2 S8 Pause Time for Comma Dial Modifier 2-2 S9 Carrier Detect Response Time 2-2 S10 Lost Carrier to Hang-Up Delay 2-2 S11 DTMF Dialing Speed 2-2 S12 Escape Code Guard Time 2-2 S13-17 Reserved 2-3 S18 Modem Test Timer 2-3 S19-24 Reserved 2-3 S24 Sleep Inactivity Timer 2-3 S25 DTR Detection 2-3 S26 RTS-to-CTS Delay Interval 2-3 S27-29 Reserved 2-3 S30 Inactivity Timer 2-3 S31-35 Reserved 2-3 S36 Protocol Negotiation Fallback 2-3 S37 Maximum DCE Speed 2-4 S38 Delay Before Forced Hang-Up 2-4 S39-42 Reserved 2-4 S43 Current DCE Speed 2-4 S44-45 Reserved 2-5 S46 Data Compression Selection 2-5 S47 Reserved 2-5 S48 V.42 Feature Negotiation Action 2-5 S49 Buffer Lower Limit 2-5 S50 Buffer Upper Limit 2-5 S51-62 Reserved 2-5 S63 Private Circuit Carrier Level 2-5 S64-81 Reserved 2-5 S82 BREAK Handling Options 2-5 S83-85 Reserved 2-6 S86 Connection Failure Cause Codes 2-6 S87-94 Reserved 2-6 S95 Negotiation Message Options 2-6 S96 Reserved 2-7 S97 V.32 Automode V.22/V.22bis Probe Timing 2-7 S98-100 Reserved 2-7 S101 Distinctive Ring Settings 2-7 S101 MNP Class 10 Options 2-8 S102 Last Ring Type Detected 2-9 S103-107 Reserved 2-9 S108 Signal Quality Selector 2-9 S109 Possible Speeds Selector 2-9 S110 Carrier Selector 2-9 S111-135 Reserved 2-10 S136 LAPM Packet Size 2-10 S137-255 Reserved 2-10 3 AT COMMAND SET 3-1 +++ On-Line Escape Sequence 3-1 A/ Repeat Last Command 3-1 AT Command Line Prefix 3-1 A Go On-Line in Answer Mode 3-1 Bn Select Protocol Compatibility 3-2 Dn Dial Telephone Number 3-2 Dial Modifiers 3-2 " Substitute Digits for Letters 3-2 , Delay Dial Sequence 3-2 ! Initiate Flash 3-3 ; Return to Command Mode after Dialing 3-3 @ Wait for Silence before Dialing 3-3 $ Wait for Bong 3-3 L Dial Last Number 3-4 P Pulse Dial 3-4 R Originate Call in Answer Mode 3-4 S Dial Stored Number 3-4 T Tone Dial 3-4 W Wait for Dial Tone 3-4 En Echo Command Characters 3-4 Hn Switch Hook Control 3-4 In Identification Request 3-4 Ln Speaker Volume 3-6 Mn Speaker Control 3-6 Nn Modulation Fallback Options 3-6 On Return to On-Line Mode 3-6 P Set Pulse Dial Mode 3-7 Qn Enable/Disable Result Codes 3-7 Sn=x Writing to S-Registers 3-7 Sn? Reading S-Registers 3-7 Sn Point to New S-Register 3-7 =x Change Contents of Referenced S-Register 3-7 ? Display Contents of Referenced S-Register 3-7 T Set Tone Dial Mode 3-8 Vn Select Result Code Format 3-8 Wn Negotiation Progress Message Options 3-10 Xn Select Extended Result Code Function 3-10 Yn Select Long Space Disconnect Function 3-10 Zn Modem Reset 3-11 &An Connect as Answering/Originating Modem 3-11 &Bn Disable Automatic Retrain 3-11 &Cn Select Data Carrier Detect (DCD) Option 3-11 &Dn Data Terminal Ready (DTR) Options 3-11 &Fn Load Factory Profile 3-12 &Gn Guard Tone Selection 3-12 &Jn Telephone Jack Selection 3-12 &Kn Local and End-to-End Flow-Control Options 3-12 &Ln Leased Line Operation 3-12 &Mn Asynchronous/Synchronous Mode Selection 3-12 &Qn Operational Mode Option 3-13 &Rn RTS/CTS Options 3-13 &Sn Data Set Ready (DSR) Options 3-13 &Tn Test Mode Options 3-13 &Un Enable Trellis Code Modulation 3-14 &V View Stored Parameters 3-15 &Wn Store User Profile 3-15 &Xn Synchronous Transmit Clock Source 3-15 &Yn Select Stored Profile on Power-Up 3-15 &Zi=n Store Telephone Numbers 3-16 $H View Help Information 3-16 AT% Commands 3-17 %C Data compression 3-17 AT%DUMBn Dumb mode 3-17 %En Line quality monitor 3-17 %L Line signal level 3-18 %Q Line signal quality 3-18 AT\ Commands 3-18 \An Maximum MNP block size 3-18 \Bn Transmit break to remote 3-18 \Cn Auto-Reliable Buffer 3-18 \En Data Echo 3-18 \Gn Modem-to-modem flow control 3-18 \Jn DTE auto rate adjustment 3-19 \Kn BREAK control 3-19 \Ln MNP block/stream mode select 3-19 \Nn Operating mode 3-20 \Qn Flow Control Options 3-20 \S On-Line Status 3-20 \Tn Inactivity Timer 3-20 \Vn MNP Result Codes 3-21 \Xn XON/XOFF Flow Control 3-21 %CCIDn Caller ID function 3-21 4 CONFIGURATION, PROTOCOLS AND GENERAL CONSIDERATIONS 4-1 Configuration Profiles 4-1 Active configuration profile 4-1 Storing configuration profiles 4-1 Establishing the power-up profile 4-1 Factory configuration profiles 4-2 Viewing the configuration profiles 4-2 Modem Configuration Guidelines 4-2 The place to start 4-2 S-Register Configuration 4-3 Modifying the S-Registers 4-3 Reading an S-Register 4-3 Modulation Protocols 4-4 File-Transfer Protocols 4-4 Modem Modes 4-5 Asynchronous Transmissions 4-5 Valid Modem Character Formats 4-5 Synchronous Transmissions 4-6 Serial Interface Pin Assignments 4-6 RS-232 Signal Definitions 4-6 Hayes AutoSync 4-7 Automatic Speed Buffering (ASB) 4-7 Macintosh Hardware Handshake Cable 4-7 Macintosh Software Handshake Cable 4-8 5 HIGH-SPEED CONSIDERATIONS 5-1 Trellis Coded Modulation 5-1 Error-Control Protocols 5-2 Data-Compression Protocols 5-2 Maximum Throughput 5-3 Data Buffering and Flow Control 5-3 Sample Modem Configurations 5-4 Universal Asynchronous Receiver/Transmitter (UART) 5-5 ProClass High Speed Serial Port (PC-HSSP) 5-6 A GLOSSARY A-1 INDEX I-1 INTRODUCTION This manual is intended to supplement the guide shipped with your unit. It is designed to provide more detailed information about the AT command set and S-Registers. Most modems utilize only a subset of all available commands. Appendix A in the manual accompanying your modem will list all of the commands available for your particular unit. The more advanced options, such as negotiation features and configuration are also included in this reference manual. Chapter 1: Introduction-Describes the use and organization of this manual. Chapter 2: S-Registers-provides a complete description of S-Registers implemented in the modem. Each active S-Register is described in detail. Chapter 3: AT Command Set-contains a complete description of modem commands. Each command is explained with a description of its use and syntax. Factory default settings are indicated where applicable. Chapter 4: Configuration, Protocols and General Considerations- explains how to configure the modem to meet your specific requirements; defines configuration profiles and how to use them and expands on the important interrelationship between your modem configuration and the setup of your communications software. Chapter 5: High Speed Considerations-introduces some of the terminology and concepts of error-control modems. This chapter describes modulation techniques, flow control, data compression, and dumb mode. Appendix A: Glossary-offers a dictionary of communications terms and their meanings. Typographical Conventions Throughout this manual, certain typographical conventions have been implemented to illustrate keyboard input and screen display dialog. Function keys and other function-specific keys are displayed in square brackets: [Enter] represents a left-pointing arrow or the word Return or Enter on the keycap. [Backspace] represents pressing the backspace key. [Esc] represents pressing the escape key. A typical dialog with the modem would be: "AT" [Enter] Keyboard entry by the user. OK Modem response displayed on screen. Typing an AT command and pressing [Enter] results in the modem responding with OK if the command is valid, or ERROR if the command is invalid. 2 S-Registers Practical Peripherals modems can use up to 256 memory storage locations- called S-Registers-to hold information about their operating environment. These S-Registers are labeled S0 to S255, inclusive. Some of the S-Registers are reserved. These either contain parameter bit maps for the internal use of the modem or are not currently in use. Generally, you should not alter or write directly to any of these reserved S-Registers because this can result in unreliable and unpredictable operation of your modem. This chapter provides you with complete definitions of each register you might have cause to read or modify and describes how that register is used. Where register options are given in a table, the factory default is marked with an asterisk (*). Note: Unless an S-Register is listed in the Operating Manual provided with your modem, it is not supported by your modem, although it appears in this document. S0 Ring to Answer On S0 sets the number of rings required before the modem picks up the telephone line to answer an incoming call (auto answer). The value can be any number between 0 and 255. S0=0 disables the auto-answer function. The AA lamp lights when S0 contains a number greater than zero. The default is 0 (zero). S1 Ring Count S1 accumulates the number of rings sensed on the telephone line. S1 resets to 0 if a ring is not sensed within any eight-second interval. When S0 contains a non-zero value between 1 and 255 and the count in S1 equals the value in S0, the modem goes off-hook to answer the call. The value of S1 can range from 0 to 255. The default value is 0 (zero). S2 Escape Code Character S2 holds the value of the ASCII character used as the modem escape code. The default is 43-the "+" character. When the modem is on-line and receives the escape sequence, it switches to command mode. S2 can be set to any value between 0 and 255. The escape code function is disabled if the value of S2 is greater than 127. S3 Carriage Return Character S3 contains the value of the ASCII character recognized as the command line terminator. The default is 13, the ASCII character for the carriage return. S3 can be set to any value between 0 and 255, but any value between 127 and 255 is seen as 127 by the modem. This parameter is not saved in nonvolatile memory with the AT&Wn command. S3 is initialized to a value of 13 when the modem is switched on or reset. S4 Linefeed Character S4 defines the value of the ASCII character recognized by the modem as the linefeed. The default is 10. S4 can be set to any value between 0 and 127, but is not saved in nonvolatile memory with the AT&Wn command. It is initialized to a value of 10 when the modem is switched on or reset. This character is sent after the carriage return character if the long form (word) result codes are selected. S5 Backspace Character This S-Register sets the value of the ASCII character recognized as a backspace. The default value is 8. S5 can be set to any value between 0 and 32. This parameter is not saved in nonvolatile memory with the AT&Wn command. It is initialized to a value of 8 when the modem is switched on or reset. S6 Wait Time before Blind Dialing This S-Register specifies the amount of time the modem waits after going off-hook before dialing the first digit of the dial string. S6 can be set to any value between 2 and 255 seconds. The default is 2 seconds. The W (wait for dial tone) modifier overrides the value contained in S6 and dials the first digit as soon as a dial tone is detected. The ATX2 and ATX4 commands enable dial tone detection and disable blind dialing. This makes the value contained in S6 irrelevant. S7 Wait for Carrier after Dial The value of S7 specifies the number of seconds the originating modem waits for carrier from the answering modem. When using the extended result code option commands ATX3 or ATX4 (factory default), S7 sets the period the originating modem waits for dial tone, quiet, or bong (calling-card prompt tone) with the W, @, and $ dial modifiers, respectively. The valid range is 1 to 255 seconds with a default of 50 seconds. S8 Pause Time for Comma Dial Modifier S8 specifies the number of seconds to pause for each comma (,) encountered in a dial string or command line. The default is two seconds, but any value between 0 and 255 is acceptable. The S8 value is stored with the AT&Wn command. S9 Carrier Detect Response Time S9 specifies the time-in 0.1 second units-that a received carrier must be present on the line before the modem recognizes it as a valid carrier and asserts the Data Carrier Detect (DCD) signal. The ability to set this value helps prevent the modem from erroneously detecting a BUSY or RING signal as a carrier. The S9 default is 0.6 seconds. The range of acceptable values is 1 to 255 (0.1 to 25.5 seconds). S10 Lost Carrier to Hang-Up Delay Specifies the time the on-line modem waits after carrier loss before it hangs up the telephone line. Setting S10 to 255 disables the hang-up function. S10 should always be greater than S9 or the modem will hang up in response to even a momentary loss of the carrier signal. The valid range of values is 1 to 255 in tenths of a second (0.1 to 25.5 seconds). The default is 1.4 seconds. S11 DTMF Dialing Speed Specifies the duration of the tones in Dual Tone Multi-Frequency (DTMF) dialing. The value can range between 50 and 255 milliseconds. The default is 95 milliseconds. This S-Register is stored with the AT&Wn command. The value of S11 has no effect on Pulse dialing. Values below 70 milliseconds can be too fast for some telephone switching equipment to process reliably. S12 Escape Code Guard Time Specifies the delay time required-before and after the entry of the escape sequence-for the modem to recognize the escape sequence as valid. This value also dictates the acceptable entry speed (inter-character time) for each escape character. The guard time is in units of 20 milliseconds (1/50th of a second), and can be set to any value between 0 and 255 (0 and 5.1 seconds). Default is 50 units (50 x 0.02 = 1 second). S13-17 Reserved A number of the modem's S-Registers are reserved for parameter bit maps and other internal uses and should remain untouched. Manipulation of these S-Registers can result in erratic and unreliable operation of your modem. S18 Modem Test Timer Establishes the duration-in seconds-in which the modem performs a diagnostic test. The default of 0 (zero) disables the test timer and allows a test to run indefinitely. S18 can be set to any value between 1 and 255 seconds. A test can be terminated from the command state at any time by issuing the AT&T0 command. S19-24 Reserved S24 Sleep Inactivity Timer This register specifies the time interval, in seconds, that the modem will operate in normal mode with no data activity before entering low-power sleep mode. The timer is reset upon any activity. The default which disables this function is zero (0). The valid range is 0 to 255. S25 DTR Detection The value of S25 specifies the time-in hundredths of a second-that DTR must be false before the modem accepts a DTR transition as valid. The action taken in response to a DTR transition is dictated by the setting of the AT&Dn command. When the modem is on-line, DTR changes for a period less than the value contained in S25 are ignored. The valid range for the contents of S25 is 0 to 255. The default value is 5. (0.05 seconds) S26 RTS-to-CTS Delay Interval This register specifies the time interval to delay between an off-to-on transition on Request to Send (RTS) and turning on Clear to Send (CTS). This value takes effect when the AT&R0 command option has been selected. This setting applies to Synchronous modes 1 (AT&Q1), 2 (AT&Q2), and 3 (AT&Q3) only. The valid range for S26 is 0 to 255, representing hundredths of a second. The default is 1. S27-29 Reserved S30 Inactivity Timer S30 specifies the period of data inactivity while on-line after which the modem hangs up the telephone line. The default which disables this function is zero (0). The valid range is 0 to 255 in ten-second intervals. This function is applicable to all buffered modes. It is not supported when the modem is configured with the AT&Q0 command. S31-35 Reserved S36 Protocol Negotiation Fallback S36 specifies subsequent action for the modem to take when the initial error-control negotiation fails. The S36 values and fallback actions are defined in the accompanying table. The default is S36=7. The selected fallback option can be forced to take place immediately with the use of S48 to disable negotiation. For example, you can force an immediate alternate protocol (MNP) connection by setting S48=128 with S36=5 or 7. Data compression selections are managed with S46. S36=0 Modem hangs up. S36=1 Attempt standard asynchronous (direct mode) connection (AT&Q0). S36=3 Attempt standard asynchronous (normal mode) connection with automatic speed buffering (AT&Q6). S36=4 Attempt V.42 alternate protocol (MNP 2-4 compatible). Hang up if negotiation fails. S36=5 Attempt V.42 alternate protocol (MNP 2-4 compatible). Fall back to standard asynchronous (direct mode) connection. S36=7* Attempt V.42 Alternate Protocol (MNP 2-4 compatible). Fall back to standard asynchronous (direct mode) connection with automatic speed buffering (ASB). S37 Maximum DCE Speed S37 selects the speed at which your modem attempts a connection with the remote modem. This is the data transmission speed across the telephone line from modem to modem. If the remote modem does not support the speed specified by S37, your modem will attempt to connect at the next lower speed. This continues until a connection is made, the options are exhausted, or the remote modem times out. The default is S37=0. See the ATBn and ATNn commands for related information. S37=0* Speed of last AT command S37=11 14,400 bps S37=3 300 bps S37=26 16,800 bps S37=5 1200 bps S37=12 19,200 bps S37=6 2400 bps S37=33 21,600 bps S37=7 4800 bps S37=29 24,000 bps S37=8 7200 bps S37=34 26,400 bps S37=9 9600 bps S37=15 28,800 bps S37=10 12,000 bps S38 Delay Before Forced Hang-Up S38 specifies the number of seconds a modem in error-control mode (AT&Q5) waits before disconnecting in response to either receiving a command to hang up the line or detecting an on-to-off transition of DTR when AT&D2 is set. This delay is to ensure that all pending data packets are sent before disconnection occurs. The default value is 20 seconds. The valid range is 0 to 255. If S38=255, the modem does not timeout but continues to attempt to deliver data until the connection is lost or all data is transferred. S39-42 Reserved S43 Current DCE Speed S43 is a read-only S-Register that contains a value defining the DCE speed of the most current connection. This S-Register is read by certain communication programs for their internal processing. This register will only return a speed when the modem is on-line. S43=0 No Connection S43=11 14,400 bps S43=3 300 bps S43=26 16,800 bps S43=5 1200 bps S43=12 19,200 bps S43=6 2400 bps S43=33 21,600 bps S43=7 4800 bps S43=29 24,000 bps S43=8 7200 bps S43=34 26,400 bps S43=9 9600 bps S43=15 28,800 bps S43=10 12,000 bps S44-45 Reserved S46 Data Compression Selection S46 is used to turn data compression ON or OFF. Your modem does not attempt negotiation for data compression if S46=0. Your modem will negotiate with a remote modem for data compression if S46=2. This is the factory default. Compression can only be enabled when the modem is operating in an error- control (EC) mode using either V.42 LAPM or the Alternate MNP protocols. S47 Reserved S48 V.42 Feature Negotiation Action S48 determines the capabilities of the remote modem and selects the specific feature and nature of subsequent actions when negotiating the initial connection. If the capabilities of the remote modem are known, S48 can be used to either tailor the negotiation to suit or bypass the negotiation phase completely. The S48=7 default enables feature negotiation. Any invalid entry is interpreted by the modem as S48=128. S48=0 Feature negotiation disabled. Bypass detection and negotiation and proceed with LAPM. S48=7* Feature negotiation enabled. S48=128 Feature negotiation disabled. Forces immediate fallback to options specified in S36. Can be used to force an MNP connection. S49 Buffer Lower Limit S49 specifies the minimum size of the buffer used in error-control or automatic speed-buffering mode. The buffer size can range from 1 to 249 bytes. The factory default is 64. (See the note after S50). S50 Buffer Upper Limit S50 specifies the maximum size of the buffer used in error-control or automatic speed-buffering mode. The buffer size can range from 2 to 250 bytes. The factory default is 220. Note: If the value of S50 is less than or equal to the value of S49, the modem automatically applies the factory defaults. S51-62 Reserved S63 Private Circuit Carrier Level S63 specifies the carrier power level, in decibels per milliwatt (dBm), for leased line operation. This S-Register specifies a carrier-level value that is not to be exceeded. The permissible range is 0 to 15 (0 to -15 dBm). The default is 0. S64-81 Reserved S82 BREAK Handling Options S82 defines the method used to send a BREAK to the remote system to get the attention of the remote modem. Expedited BREAKs are sent immediately, before transmission of any pending data. Destructive BREAKs are also sent immediately and any pending data is destroyed. Timed BREAKs preserve the time BREAK is pressed, rounding to the nearest 10 milliseconds. Sequenced BREAKs are sent in sequence with the pending data without destroying the data. S82=3 Expedited, timed BREAK signal. Data integrity is maintained before and after the BREAK signal. S82=7 Destructive timed BREAK signal. Data in process is destroyed. S82=128* In-sequence, timed BREAK signal. Data integrity is maintained before and after the BREAK signal. S83-85 Reserved S86 Connection Failure Cause Codes When the modem fails to make a connection and returns the NO CARRIER result code, a value is written in S86 which defines the cause of the failed connection. S86 records the first event that causes a NO CARRIER message to occur. S86=0 Normal connect termination. No error occurred. S86=4 Physical carrier loss. S86=5 V.42 feature negotiation failed to detect an EC (error control) modem at remote end. S86=6 Remote EC modem did not respond to negotiation message. S86=7 Remote modem is a synchronous-only modem. S86=8 Modems could not find a common framing technique. S86=9 Modems could not find a common protocol. S86=10 Incorrect feature negotiation message sent by remote modem. S86=11 Synchronous information (data or flags) not received from the remote modem. Modem waited 30 seconds before hanging up. S86=12 Normal disconnect initiated by remote modem. S86=13 Remote modem did not respond to repeated message. After ten attempts, the local modem terminated the call. S86=14 Protocol violation occurred. S86=15 Compression failure. S87-94 Reserved S95 Negotiation Message Options S95 enables various result messages pertaining to an error-controlled connection. This S-Register does not alter the way the connection is negotiated, it just enables extended messages. Changing the ATWn command does not alter the setting in S-Register S95. The ATWn command can be used, however, to obtain some of the same negotiation progress displays. For example, S95=0 and ATW1 produce the same display as S95=12 and ATW0. Both configurations display the CARRIER at the DCE speed, the PROTOCOL in effect, and the CONNECT at the DTE speed. S95 values can be added together to obtain the desired message response. For example, S95=44 (4+8+32=44) sends the CARRIER, PROTOCOL, and COMPRESSION messages to your screen in addition to the CONNECT message. S95=0* Default setting. Extended messages disabled. S95=1 Use DCE (modem-to-modem) speed rather than DTE (computer-to- modem) speed when reporting CONNECT messages. S95=2 Append /ARQ to CONNECT result message when an error- controlled (EC) connection is made. S95=4 Enable CARRIER messages. S95=8 Enable PROTOCOL messages. S95=32 Enable COMPRESSION messages. S96 Reserved S97 V.32 Automode V.22/V.22bis Probe Timing S97 sets the duration of the signal-in 0.1 second units-used by the modem in the answer mode during a V.32 automode handshake to determine if the calling modem is a V.22 or V.22bis-type modem. The value of this S-Register also sets the time during which the modem will reject the V.22/V.22bis probe signal when executing the V.32 automode handshake in originate mode. The register value can range from 15 to 70-representing 1.5 to 7.0 seconds. The default value of 30 (3.0 seconds) provides the timing necessary to connect to most V.22bis-compatible modems. When compatibility with V.32 late connecting modems is a primary requirement, S97 should be set to 15. This value is also compatible with the timing specified in the ITU-T recommendation V.22bis. S98-100 Reserved S101 Distinctive Ring Settings Distinctive ring is an optional feaure provided by the telephone company for a nominal charge. Distinctive ring allows two telephone numbers to access one telephone line with differentiating rings. The known ring patterns are labeled Type A through Type F. A seventh category, Type G, is used to identify a pattern not conforming to the known six. The following list displays the call patterns supported by the modem. TYPE A __----------_________________ typical desk phone LONG TYPE B __----------xxxx______________ typical home phone LONG TYPE C __----------___----------________ typical distinctive ring LONG LONG and British ring pattern TYPE D __------___------___---------____ SHORT SHORT LONG TYPE E __------___---------___------____ SHORT LONG SHORT TYPE F __---_____---------____---____ SHORT LONG SHORT S-Register S101 specifies the ring pattern the modem will recognize. Any combination of rings can be specified by adding the bit designators. If S101=36,for example, 36=32+4, which specifies that the modem answers ring patterns C and F, and sends the RING response to the monitor screen. Another example would be S101=164, where 164=32+4+128, specifies the same ring patterns and RING C or RING F responses depending on the actual ring received. S101=0* Return RING for any ring pattern detected. S101=1 Only respond to ring pattern A, show RING if ring happens. If ATS101=129, where 129 = 128+1, show RING A. S101=2 Only respond to ring pattern B, show RING if ring happens. If ATS101=130, where 130 = 128+2, show RING B. S101=4 Only respond to ring pattern C, show RING if ring happens. If ATS101=132, where 132 = 128+4, show RING C. S101=8 Only respond to ring pattern D, show RING if ring happens. If ATS101=136, where 136 = 128+8, show RING D. S101=16 Only respond to ring pattern E, show RING if ring happens. If ATS101=144, where 144 = 128+16, show RING E. S101=32 Only respond to ring pattern F, show RING if ring happens. If ATS101=160, where 160 = 128+32 show RING F. S101=64 Only respond to ring pattern G, show RING if ring happens. If ATS101=192, where 192 = 128+64, show RING G. S101=128 Shows ring pattern type when ring occurs. S101=255 Responds to all ring patterns and returns ring type, as follows: RING A for ring pattern A RING B for ring pattern B RING C for ring pattern C RING D for ring pattern D RING E for ring pattern E RING F for ring pattern F RING G for unknown ring pattern S101 MNP Class 10 Options (2400EFX/2400EFXSA modems only) Microcom Networking Protocol (MNP) Class 10 allows your PM2400EFX or PM2400EFXSA to operate in a cellular telephone environment. S-Register S101 is used to determine whether or not your modem attempts to make MNP 10 connections and the manner in which such connections are made. If S101=0, MNP Class 10 is disabled. If MNP Class 10 (extended) service is enabled, your modem will investigate the remote modem's MNP 10 capabilities and determine if a LAPM connection can be converted to an MNP 10 connection for transmissions over a cellular telephone network. How the connection is established depends on the setting of S101. S101=0* MNP Class 10 service disabled. S101=1 MNP Class 10 services enabled. Transmit level fixed at =10dBm. Negotiation occurs at mutually-agreed line speed. S101=3 MNP Class 10 services enabled. Transmit level adjusted during retrain/speed shift. Negotation occurs at mutually-agreed line speed. S101=5 MNP Class 10 services enabled. Transmit level fixed at -10dBm. Negotiation occurs at 1200 bps. S101=7 MNP Class 10 services enabled. Transmit level adjusted during retrain/speed shift. Negotiation occurs at 1200 bps. S102 Last Ring Type Detected When the modem detects a call and returns the RING result code, a value is written in S102 which defines the type of ring detected. S102 records the last event that caused a RING message to occur. S102 is a read-only register. S102=1 Ring pattern A S102=2 Ring pattern B S102=4 Ring pattern C S102=8 Ring pattern D S102=16 Ring pattern E S102=32 Ring pattern F S102=64 Ring pattern G S103-107 Reserved S108 Signal Quality Selector This S-Register sets the signal quality required for the modem to handshake at the highest designated V.32bis speed and for automatic rate renegotiation. If, during carrier handshake, the modem determines that the signal quality is less than that specified by S108, the modem will attempt to connect at the next lower speed indicated by S109-unless the ATN0 command has been selected. If the ATN0 command has been selected, only the speed indicated by S-Register S37 can be used. S108=0 No limit. S108=1 * Low quality. S108=2 Medium quality. S108=3 High quality. S109 Possible Speeds Selector S109 controls the speeds available for V.32bis, V.FC and V.34 carrier handshakes. This permits you to disable speeds lower than the highest carrier speed while enabling the highest carrier speed or other carrier speeds. S37 selects the highest carrier speed for the initial connection. If the ATN0 command is selected, the carrier speed specified by S37 and one of the speeds specified by S109 must match. The modem will connect only at that carrier speed. While the modem is in V.32bis, V.FC and V.34 mode, the S37 and the ATN0 command settings do not affect the modem speed during retrain or rate renegotiation procedures. S109=1 * Reserved S109=64 * 16,800 bps S109=2 * 4800 bps S109=128 * 19,200 bps S109=4 * 7200 bps S109=256 * 21,600 bps S109=8 * 9600 bps S109=512 * 24,000 bps S109=16 * 12,000 bps S109=1024 * 26,400 bps S109=32 * 14,400 bps S109=2048 * 28,800 bps Note that the factory default causes all speed options shown in the table (and applicable to your modem) to be selected. Note: If speed negotiation is disabled by the ATN0 command, and S37 indicates a V.32bis speed that is not enabled by S109, no connection will be made. S110 Carrier Selector The V.32 and V.32bis carrier handshake procedures are compatible. The rate sequence contains bit combinations that specify the procedure to be used. V.FAST Class uses different rate sequence bit combinations and are not compatible with V.32 and V.32bis carrier handshake procedures. S110 provides control of that selection for users who want to limit carrier handshake procedure to that specified by V.32, V.32bis, V.FC, V.34 or to disable automatic rate re-negotiation (rate changes initiated by the modem based on signal quality). When S110=0, V.32 handshake procedure is followed, rate re-negotiation allowed by V.32bis is disabled, and the AT&Un command determines whether or not trellis encoding is enabled. When S110=1, V.32bis handshake is enabled, but not automatic re-negotiation. The modem responds to a rate re-negotiate request from the remote end. When S110=2, V.32bis handshake and automatic rate re-negotiation are enabled. When S110=3, V.FAST Class handshake is enabled but not automatic re- negotiation. The modem responds to a rate re-negotiate request from the remote end. When S110=4, V.FAST Class handshake and automatic rate re-negotiation are enabled. When S110=5, V.34 handshake is enabled but not automatic re-negotiation. The modem responds to a rate re-negotiation request from the remote end. When S110=6, factory default, V.34 handshake and automatic rate re-negotiation are enabled. S111-135 Reserved S136 LAPM Packet Size S136 controls the packet size being sent during a LAPM connection. The size options are S136=0 for 128 bytes per packet, S136=1 (default) for 256 bytes, and S136=2 for 512 bytes. These options change the maximum packet size that LAPM will attempt to negotiate with the remote modem. Better throughput may be achieved with the larger packet size. S137-255 Reserved 3 AT Command Set This chapter describes the complete command set used by Practical Peripheral modems. The commands are listed alphabetically. Complete details are provided for each command, including the meaning of the command, its use and its format. When command options are listed in a table, an asterisk (*) indicates the factory defaults configured in response to the AT&F or AT&F0 command. All commands except the first two described must be preceded by the AT command prefix, and followed by a terminating carriage return. Note: Unless a command is listed in the Operating Manual provided with your modem, it is not supported by your modem, although it appears in this document. +++ On-Line Escape Sequence The escape sequence is used to return to command mode from on-line mode. The default escape code character is ASCII 43-the "+" character. This is defined by the contents of S-Register S2. The escape function is disabled if the value of S2 is greater than 127. When the modem is on-line, the command processor monitors the data stream for the escape sequence characters (defined by the value in S2) within the time constraints set by S-Register S12. When a valid escape sequence is detected, the modem switches from on-line to command mode. The escape sequence is not preceded by the AT command prefix, nor does it require a terminating carriage return. A/ Repeat Last Command This command is the second of the two commands that do not require the AT command line prefix, nor does it need to be followed by a carriage return. The primary function of the A/ command is to repeat a preceding dial string that has failed to complete a connection due, for example, to a BUSY line. This command re-executes the command line stored in the command buffer when the preceding command was entered. AT Command Line Prefix AT is the command line prefix. It must be used before all of the following commands. This prefix tells the modem that the next characters are a modem command. Only the two commands listed above can be entered without the AT prefix. All modem commands are entered when the modem is in command mode. Any commands entered when the modem is in on-line mode are interpreted as data and will not produce the expected result. Each time the AT command is entered, the modem's serial port speed and data word format are set to that of the local terminal. A Go On-Line in Answer Mode The ATA command causes the modem to begin the call answer process regardless of the contents of S-Register S0. This command must be either the only command on the command line, or the last command in a command line. Upon receiving the A command, the modem takes the telephone line off-hook and issues the answer tone. One of the following three results are possible: 1. A connection is established and the normal CONNECT message is displayed. 2. A NO CARRIER message is returned. This occurs if a connection is not made before the time specified in S7 expires, or the process is aborted by sending a character to the modem from the local terminal. 3. An ERROR message is displayed. This occurs if this command is entered while the modem is already in data (on-line) mode. The modem responds with OK if the process is aborted by a change in the Data Terminal Ready (DTR) signal when the AT&D2 or AT&D3 command setting is active. Bn Select Protocol Compatibility The ATBn command selects the modulation protocol the modem will use. The choices are listed in the following tables. Protocols for 1200 bps B0 Initiate calls using ITU-T V.22 at 1200 bps. B1* Initiate calls using Bell 212A at 1200 bps. B2 Enable ITU-T V.23 with transmit 75 bps, receive 1200bps. B3 Enable ITU-T with transmit 1200 bps, receive 75 bps. Protocols for 300 bps B15 Initiate calls using ITU-T V.21 at 300 bps. B16* Initiate calls using Bell 103 at 300 bps. Protocols for28800 bps B75 Initiate calls using ITU-T V.32bis at 14400 bps. B76* Initiate calls using V.FAST Class at 14400 bps. Dn Dial Telephone Number The ATDn command is used to dial a specific number. The n represents an ASCII string composed of dial digits and dial modifiers (see below) and must not exceed the 255-character command buffer limit. Spaces, hyphens, and parentheses can be used for clarity. These are ignored and are not included as part of the 255-character limit. The modem can be used with either pulse or tone dialing systems. For pulse dialing, the dial digits are 0 through 9 only. For tone dialing, the digits include 0 through 9, A, B, C, D, and the symbols # and *. Dial Modifiers The following dial modifiers are recognized only when they are contained in a dial string that follows the ATD command. " Substitute Digits for Letters Letters (except Q and Z) enclosed within the double quotes (") modifier are converted to their numerical equivalents as found on the standard telephone. For example, the command line ATDT"FLOWERS" is converted to ATDT3569377 , Delay Dial Sequence When the comma (,) modifier is encountered, the modem pauses for a programmed number of seconds before processing the next symbol in the string. The programmed pause is contained in S-Register S8 and is factory-set at 2 seconds. The , modifier is most often used when dialing an outside number through a switchboard. It is inserted after the digit used to obtain an outside line. This is to allow sufficient time for the dial tone to begin before the modem dials the telephone number. If you prefer, the W modifier can be used for this purpose in place of the , modifier. The , modifier is also used after the code for disabling call waiting. For example: ATDT*70,1-800-555-1234 The , modifier can also be used in the command line, to insert a delay between commands being entered. ! Initiate Flash The ! modifier is the equivalent of pressing the hook control switch for 1/2 second on many of today's telephone systems. ; Return to Command Mode after Dialing If you need to dial a number that is too long to be contained within the command buffer, use of the ; modifier allows you to separate this string into multiple dial commands. All but the last command must end with the ; modifier. Each line must be followed by a carriage return. For example: Keyboard: ATDT95551234; Display: OK ATDT123456789; OK ATDT1234567890 Note the absence of the ; modifier after the last dial command. @ Wait for Silence before Dialing Some telephone systems do not offer a dial tone when accessed. While there can be a dial tone before the system access number, once the access number is reached and answers, there could be only silence on the line. The @ modifier placed in a dial string tells the modem to wait for the time specified in S-Register S7 for one or more rings followed by 5 seconds of silence before processing the next symbol in the string. The factory default setting for S7 is 50 seconds. For example: AT DT 555-1234 @ 123456789 W 800-555-4321 In this example, the modem dials the local access number of a telephone service and waits for one or more rings during the 50 seconds specified by S-Register S7. This is followed by 5 seconds of silence. If, after 50 seconds, the silence is not detected, the modem hangs up and sends a NO ANSWER result code to the terminal. If the modem detects a busy signal, it sends a BUSY result code to the terminal. If, on the other hand, 5 seconds of silence is detected, the modem processes the remaining numbers in the dial string. The next set of numbers in the sample dial string is the security access code for a private long distance service. Once these numbers have been dialed, the W code has been inserted to wait for a dial tone before dialing the destination telephone number. $ Wait for Bong The $ modifier tells the modem to wait for the calling-card prompt tone (bong) before dialing the remaining numbers in the dial string. This situation arises when placing a calling-card telephone call. The bong from the telephone service indicates readiness to accept a calling-card number for billing purposes. The time period to wait is stored in S-Register S7. The factory default for S7 is 50 seconds. In the following example, the command line instructs the modem to tone dial 0 (800) 555-1234. The zero (0) preceding the area code indicates that this is a calling-card call. The $ symbol instructs the modem to wait the period of time specified by the contents of S7 for the telephone service's bong tone, and then transmit the telephone calling-card identification sequence that follows the $ symbol. ATDT 0 (800) 555-1234 $ (800) 555-4321 9999 L Dial Last Number The ATDL command redials the last telephone number dialed by the modem. It differs from the A/ command in that the ATDL command does require the AT command prefix and simply dials a telephone number; it does not send the entire command buffer as the A/ command does. P Pulse Dial When the P modifier is included in the command line, the modem pulse dials the numbers that follow. See also the ATP command. R Originate Call in Answer Mode The R modifier is used to allow your modem to call an originate-only modem by forcing the call into answer mode. The R modifier must be the last character in the dial string before the carriage return. S Dial Stored Number The S modifier instructs the modem to dial a number previously stored in response to the AT&Zn command. The command to dial a stored number is ATDS=n, where n=0, 1, 2, or 3 representing the specific location in non-volatile memory in which you stored the number with the AT&Zn command. For example, ATDTS=3, tone dials the number stored in location 3. T Tone Dial When the T modifier is included in the dial string, the modem tone dials the numbers that follow. See also the ATT command. W Wait for Dial Tone The W modifier tells the modem to wait a predefined length of time for a dial tone before dialing the remaining numbers in the dial string. The predefined period to wait is stored in S-Register S7. The default is 30 seconds. En Echo Command Characters When your modem is in command mode and receiving command input from your computer, the ATEn command controls the echo of the characters back to the computer. To disable command echo, type ATE0 or ATE. To enable command echo, type ATE1. This is the factory default. If you type a command that does not appear on the terminal screen, your software is set to expect character echo from the remote system, so use the ATE1 setting. If you type a command that appears with the characters duplicated, LLIIKKEE TTHHIISS, use the ATE0 setting. Hn Switch Hook Control The ATH or ATH0 command causes the modem to hang up (go on-hook). To go off- hook use ATH1. In Identification Request To request your modem's product code, use either the ATI0 or ATI command. The modem sends the product code as a three-digit string in the form NNNx where N stands for the speed of your modem, and x stands for the revision level of your modem followed by a carriage return and linefeed character. The ATI1 command returns the ROM checksum as three ASCII numeric characters followed by a carriage return and linefeed. The ATI2 command performs a checksum calculation on the modem's read-only memory (ROM) and returns either two OK responses or an ERROR response. The ATI3 command returns the firmware revision number of your modem in a form similar to: Modem Model [XXX] Version x.xx (c) Practical Peripherals Inc., 19xx ATI4 returns a series of numbers based on a bit map. These numbers are used by some software packages to identify modem feature availability. The ATI6 command provides you with information concerning link statistics and connection details during or at the termination of the current connection. To display the information during the course of the current connection, you will need to enter the +++ escape sequence to force the modem into command mode before the ATI6 command can be effective. The following are descriptions of the categories on the screen: Characters Sent: Number of characters sent by your modem. Characters Received: Number of characters received by your modem. Octets Sent/Received: Octets are compressed data units. Their presence indicates that data compression occurred during the transmission. This category will be displayed only when the AT&Q5, AT&Q8, or AT&Q9 command has been issued for this connection. Packets Sent/Received: Number of data packets (blocks) either sent by your (local) modem or received from the other (remote) modem. NAKs Sent/Received: Number of packets requiring retransmission to or from your modem due to transmission errors. Rate Sent/Received: Total number of rate renegotiations requested, followed by the number of requests for a higher DCE rate, and finally, the number of requests for a lower DCE rate. Entries in the Sent column were sent by your local modem, those in the Received column were requested by the remote modem. Retrain Sent/Received: Total number of carrier retrains requested, followed by the number of requests for a higher DCE rate, and finally, the number of requests for a lower DCE rate. Entries in the Sent column were sent by your local modem, those in the Received column were requested by the remote modem. Last Number Called: Remote location to which you were, or are connected. Connection Time: Duration between connection and disconnection. Mode: The operational mode of the modem during the connection. DCE Speed: Data transmission rate between your modem and the remote modem. Protocol: This can show LAPM, MNP, or None depending on the error-control protocol negotiated during the handshaking sequence. DTE Speed: Data transmission rate between your modem and your computer/ terminal. Compression: Denotes the type of data compression implemented during the connection. DTE Parity: Indicates the type of data parity checking implemented over the link between your modem and your computer/terminal. Flow Control: Operational flow control of the modem during the connection. Call Termination: Why the modem hung up. This reflects the value of S-register S86 and can contain one of the following reasons: Normal Termination Physical Carrier Loss No V.42 At Remote Remote Refused Feature Negotiation Remote Modem Is Synchronous Only No Common Framing Technique No Common Protocol Cannot Support Remote Features No Sync. Flags From Remote Normal Disconnect By Remote Modem Local Retry Count Exceeded Protocol Violation Occurred Compression Failure Ln Speaker Volume The speaker volume for your modem is controlled with the ATLn command. The default is ATL2 for medium speaker volume. See also the ATMn command which enables and disables the speaker entirely. L0 Low speaker volume. L1 Low speaker volume. L2* Medium speaker volume. L3 High speaker volume. Mn Speaker Control The ATMn command is used to enable or disable the speaker according to your specific requirements. The default is ATM1. M0 Speaker always OFF. M1* Speaker ON until data carrier is detected. M2 Speaker always ON. M3 Speaker ON after dialing until data carrier is detected. Nn Modulation Fallback Options The ATNn command determines modem action when the speed of the remote modem is different than that of the local modem. This command can be used to force a connection at a specified speed. The default is ATN1. N0 When originating or answering, modem handshakes only at the speed specified in S-Register S37. N1* When originating, allows negotiation of a common modulation protocol at the highest line speed supported by both modems. Negotiation begins at the DCE speed set in S37, falling back to slower speeds as necessary. When answering, falls back from V.FAST Class to V.32bis or V.32, then to V.22bis, V.22, to Bell 212A, V.21/Bell 103, and V.23, as required. On Return to On-Line Mode When your modem has been switched to command mode in response to either a transition of DTR with AT&D1 active or the use of the escape sequence to exit from an active connection, you can return to on-line mode using the ATO or ATO0 command. The ATO1 command returns the modem to on-line mode and begins an equalizer retrain sequence. The ATO1 command can be used to reduce errors attributable to loss of equalization when the bit error rates are excessive. When AT&C1 is selected and the modem initiates a retrain procedure, the CD light will flash during the duration of the retrain procedure. The ATO3 command returns the modem to on-line mode and begins a V.32bis rate renegotiation procedure. The new rate options are those specified by the setting of S-Register S109, which must be set to the required rate prior to the ATO3 command being entered. Neither the contents of S-Register S37 nor the setting of the ATNn command affect the rate renegotiation procedure. P Set Pulse Dial Mode The ATP command sets the modem to dial in the pulse mode. Pulse dialing is the factory default. See the section on dial modifiers for more information. Qn Enable/Disable Result Codes The ATQn command controls the issuing of result codes that acknowledge both the AT commands and call-status result codes such as OK, BUSY, and RING . The factory default setting of ATQ or ATQ0 enables the result code function. ATQ1 will stop the modem from sending result codes to the terminal. Result codes can also be sent in an abbreviated form using the ATV command described later in this chapter. Q0* Result codes enabled. Q1 Result codes disabled. Q2 Modem returns result codes when originating a call, but does not return result codes when answering a call. Sn=x Writing to S-Registers In the command format ATSn=x, the value of n indicates the S-Register number, while the value of x ranges from 0 to 255, and represents the S-Register value. Thus, ATSn=x sets S-Register n to the value x. S-Registers are modem memory locations provided to hold modem configuration parameters. The Sn=x command is used to modify these S-Registers. Please refer to Chapter 2 for a detailed description of each S-Register. Sn? Reading S-Registers The command ATSn?, where n indicates a specific S-Register, causes the contents of S-Register Sn to be sent to the monitor screen. Not all numbered S-Registers are implemented. See Chapter 2 for more details. Sn Point to New S-Register The ATSn command instructs the modem to change the value of its S-Register pointer to the value of n. The variable n currently accepts a value between 0 and 255. This is used in conjunction with the AT=x and AT? commands. =x Change Contents of Referenced S-Register The AT=x command, where x=0 to 255, sets the last-referenced S-Register to the value of x. This command is used in conjunction with the ATSn command. ? Display Contents of Referenced S-Register The AT? command causes the modem to display the contents of the last- referenced S-Register. This command is used in conjunction with the ATSn command. The ATSn, AT?, and AT=x commands are redundant. What can be achieved with these three commands can be achieved with the ATSn? and ATSn=x commands using fewer keystrokes. T Set Tone Dial Mode The ATT command sets the modem to dial in tone mode. See the section on dial modifiers for more information. Vn Select Result Code Format Although your modem is factory set for long-form (word) result codes, you can choose to use short-form (numeric) result codes. Short-form result codes contain only one or two digits and can be useful when your modem is controlled by a software terminal emulation program using script files. Type ATV or ATV0 to select the short-form result codes. Type ATV1 either to reset the factory default after a change has been made or to select the long-form result codes. All result codes are ASCII values. All long-form result codes are preceded and terminated with both a carriage return and a linefeed character. Short-form codes are terminated with a carriage return character. When you issue a command, the modem responds with either OK or ERROR to indicate that it either understands and can act upon your command or that it does not recognize the command as valid. With manipulation of the ATV and ATX commands, you can tailor call-progress messages to suit your application. The ATWn command and the setting of S95 does the same with the negotiation progress messages. Negotiation progress messages are those with a numerical value of 40 or greater. Note that there are four commands, two dial modifiers, and one S-Register that are directly applicable to the result codes generated by the modem. These are the ATQn, ATVn, ATWn, and ATXn commands, the W and @ dial modifiers, and S95. Result Code Messages Long Form Short Form Meaning OK 0 Command OK CONNECT 1 Connect at 300 bps RING 2 Ring detected NO CARRIER 3 No carrier detected ERROR 4 Error in format CONNECT 1200 5 Connect at 1200 bps NO DIALTONE 6 No dial tone detected BUSY 7 Busy signal NO ANSWER 8 No answer (with @ only) CONNECT 2400 10 Connect at 2400 bps CONNECT 4800 11 Connect at 4800 bps CONNECT 7200 24 Connect at 7200 bps CONNECT 9600 12 Connect at 9600 bps CONNECT 12000 25 Connect at 12,000 bps CONNECT 14400 13 Connect at 14,400 bps CONNECT 16800 26 Connect at 16,800 bps CONNECT 19200 14 Connect at 19,200 bps CONNECT 21600 60 Connect at 21,600 bps CONNECT 24000 29 Connect at 24,000 bps CONNECT 26400 34 Connect at 26,400 bps CONNECT 28800 15 Connect at 28,800 bps CONNECT 38400 28 Connect at 38,400 bps CONNECT 57600 18 Connect at 57,600 bps CONNECT 115200 31 Connect at 115,200 bps CONNECT 230400 65 Connect at 230,400 bps CARRIER 300 40 Carrier detected at 300 bps CARRIER 1200 46 Carrier detected at 1200 bps CARRIER 2400 47 Carrier detected at 2400 bps CARRIER 4800 48 Carrier detected at 4800 bps CARRIER 7200 49 Carrier detected at 7200 bps CARRIER 9600 50 Carrier detected at 9600 bps CARRIER 12000 51 Carrier detected at 12,000 bps CARRIER 14400 52 Carrier detected at 14,400 bps CARRIER 16800 53 Carrier detected at 16,800 bps CARRIER 19200 54 Carrier detected at 19,200 bps CARRIER 21600 38 Carrier detected at 21,600 bps CARRIER 24000 37 Carrier detected at 24,000 bps CARRIER 26400 36 Carrier detected at 26,400 bps CARRIER 28800 55 Carrier detected at 28,800 bps COMPRESSION: MNP5 66 MNP/5 data compression enabled COMPRESSION: V.42BIS 67 V.42bis data compression enabled COMPRESSION: NONE 69 Data compression disabled PROTOCOL: NONE 70 Standard asynchronous mode PROTOCOL: LAPM 77 V.42 error control mode: LAPM PROTOCOL: MNP 80 Alternate EC protocol: MNP Wn Negotiation Progress Message Options A subset of the result code messages can be enabled to provide information about carrier speed, error-control protocol, and data compression. The ATWn command should not be confused with the W dial string modifier. The ATWn command does not affect the negotiation process; it merely enables another set of informational messages. ATWn works in conjunction with S-Register S95 to determine the form and content of negotiation progress messages returned by the modem. See Chapter 2 for more information on S95. W0* Negotiation progress messages disabled. W1 Negotiation progress messages enabled. CONNECT messages reflect the DTE (terminal-to-modem) speed. W2 Do not return negotiation progress messages. Return CONNECT messages that reflect the DCE (modem-to-modem) speed. Xn Select Extended Result Code Function The ATXn command determines if the modem responds to dial tone and busy signals and how it displays result codes for CONNECT messages. When the modem ignores dial tone, it waits for the duration specified by the contents of S6 (2 seconds default) and dials regardless of the presence or absence of dial tone. This is called blind dialing. The ATX or ATX0 command sets the modem to the 300 bps compatibility mode. Once a satisfactory connection has been made, the modem sends a CONNECT message to the terminal display. In this mode the modem does not recognize a dial tone or a busy signal. Instead, the modem blind dials after pausing for the number of seconds prescribed by S-Register S6. When the ATX1 command is issued, the modem sends CONNECT (Bell 103 mode), CONNECT 1200, CONNECT 2400, or CONNECT nnnn at whatever speed is appropriate and in accordance with the ATWn command and the setting of S95 when a connection is made. In this mode, the modem does not recognize either a dial tone or a busy signal. As above, the modem blind dials using the pause dictated by S-Register S6. The ATX2 command sends the same CONNECT messages within the same constraints described above. With ATX2, however, the modem waits for a dial tone before dialing. If a dial tone is not detected within 5 seconds, the NO DIALTONE result code is displayed on your monitor screen. While the modem recognizes a dial tone in this command configuration, it does not recognize a busy signal. The ATX3 command follows the same format for CONNECT or CONNECT nnnn messages as described for ATX1 and ATX2 with the speed determined by the settings of ATWn or S95. With ATX3, the modem does not recognize a dial tone and blind dials as described above. This command configuration does, however, recognize a busy signal. The BUSY result code is displayed on your monitor if a busy signal is detected. Using the ATX4 command, the modem sends the appropriate CONNECT, CONNECT 1200, or CONNECT nnnn message to your terminal or computer monitor once a satisfactory connection has been established. The modem waits for a dial tone before dialing. If a dial tone is not detected within 5 seconds, a NO DIALTONE result code is displayed. If a busy signal is detected, a BUSY result code is displayed. ATX4 is the factory default setting. The ATXn Command Summary Table in Appendix A of the manual furnished with your modem, further illustrates these commands and associated result codes. Yn Select Long Space Disconnect Function When you enable this function by entering ATY1, the modem disconnects whenever it receives a BREAK from the remote modem for a period of at least 1.6 seconds. The modem sends a BREAK for 4 seconds before disconnecting in response to receiving an ATH command or detecting an ON-to-OFF transition on DTR if the AT&D2 option is selected. This function is disabled at the factory. If you have enabled it, and want to return to the original default setting, type either the ATY or ATY0 command. Zn Modem Reset The ATZn command resets the modem, causing the modem to break any existing connection. One of the two configuration profiles stored in nonvolatile memory is then written over the active parameter profile of the modem. The parameter n defines either Stored Profile 0 or 1. &An Connect as Answering/Originating Modem The AT&A0 command forces the modem to connect as an answering modem when auto-answering. This is the factory default. When AT&A1 is used, the modem connects as an originating modem when auto- answering. &Bn Disable Automatic Retrain The AT&Bn command controls the automatic retrain capability of the modem. The AT&B1 factory default setting enables this capability. AT&B0 disables the automatic retrain capability. AT&B2 enables the capability, but if no improvement in line quality occurs within the time specified by S-Register S7, the connection is terminated. V.32, V.32bis, and V.FAST Class modems continually monitor line quality during a call. When the line degrades to a certain level, the modem can request a retrain of the equalizer, allowing both modems to adjust to the prevailing line condition. This can improve data integrity and throughput. The retrain process takes several seconds and disrupts any current data transfers. When AT&C1 is selected and the modem initiates a retrain procedure, the CD light will flash for the duration of the retrain procedure. &Cn Select Data Carrier Detect (DCD) Option The AT&C0 command forces the Data Carrier Detect (DCD) signal to be ON regardless of the state of the remote modem's data carrier. This is the factory default. This setting (along with AT&D0 to ignore DTR) is needed by a few dedicated dumb terminals only. In the case of AT&C1, DCD tracks the state of the data carrier from the remote modem. An ON condition of DCD indicates the presence of a carrier. This setting suits most microcomputer communications programs. When AT&C1 is selected and the modem initiates a retrain procedure, the CD light will flash during the duration of the retrain procedure. AT&C2 sets DCD ON except during the disconnect process in &Q0 and &Q6 modes only. &Dn Data Terminal Ready (DTR) Options The AT&Dn commands control modem response to the Data Terminal Ready (DTR) signal and determine how the modem responds to a transition of the DTR signal from the computer. When on-line, a DTR transition that does not equal or exceed the time value stored in S-Register S25 is ignored by the modem. The factory default for S25 is 5 (0.05 seconds). &D0* Ignore status of the DTR signal from the computer. &D1 Monitor DTR and, upon an ON-to-OFF transition of the DTR signal, enter command mode. &D2 Monitor DTR and, upon an ON-to-OFF transition of the DTR signal, hang up the line and enter command mode. &D3 Monitor DTR and, upon an ON-to-OFF transition of the DTR signal, hang up, reset the modem and assume the initialization state. This overwrites the active configuration profile (ACP) with the appropriate stored profile. &Fn Load Factory Profile The AT&Fn command is used to load one of the available sets of factory default parameters from ROM into the Active Configuration Profile. This action completely replaces the parameters in the ACP with those that comprise the chosen factory configuration. The result is not the same as that obtained with a power cycle or the ATZn command. The following table shows the essential differences between these factory settings. All other default settings are the same. &Fn Application Key Settings &F0 Hayes-compatible settings &C0&D0&K3 &F1 IBM-compatible settings &C1&D2&K3 &F2 Macintosh software handshake settings &C1&D2&K4 &F3 Macintosh hardware handshake settings &C1&D0&K3 &Gn Guard Tone Selection The modem generates the guard tone selected by this command according to the parameter supplied (DPSK modulation modes only). &G0* Disable guard tone. &G1 Disable guard tone. &G2 Enable 1800 Hz guard tone. &Jn Telephone Jack Selection The modem accepts and acknowledges the AT&Jn commands. Telephone jack type selection is not supported. This modem supports only the standard, RJ-11 telephone jack. &Kn Local and End-to-End Flow-Control Options When the DTE (computer-to-modem) and DCE (modem-to-modem) data speeds are not the same, there is a requirement for data buffering and controlling the flow of data between modem and computer. The AT&Kn command controls how local flow control between DTE (your computer) and DCE (the local modem) is handled. As can be seen from the following table, the AT&K6 and AT&K7 commands provide both local and end-to-end flow control. These parameters are applicable only when automatic speed buffering (ASB) is active (AT&Q6). When an error-control (EC) protocol is in effect, the protocol handles DCE-to-DCE flow control. &K0 Disable local flow control. &K1 Enable RTS/CTS hardware local flow control. &K2 Enable XON/XOFF software local flow control. &K3* Enable RTS/CTS hardware local flow control. &K4 Enable XON/XOFF software local flow control. &K5 Enable transparent XON/XOFF &K6 Enable XON/XOFF local flow control with pass through. &K7 Enable RTS/CTS local flow control with XON/XOFF pass through. &Ln Leased Line Operation The AT&L or AT&L0 command, the factory default, notifies the modem that it is connected to a standard dial-up line. The AT&L1 command notifies the modem that it is connected to a leased line. &L0* Select Dial up line operation. &L1 Select Leased line operation. &Mn Asynchronous/Synchronous Mode Selection The AT&Mn commands are the same as the AT&Qn commands described in the following section. &Qn Operational Mode Option The AT&Qn command is used to select the operational mode of the modem in accordance with the accompanying table. Synchronous Mode 1 (&Q1) requires a synchronous interface card supporting both asynchronous and synchronous operation through the same port. Synchronous Modes 2 and 3 (AT&Q2 and AT&Q3) require a synchronous interface card in your computer or terminal that supports synchronous operation only. In error-control mode (&Q5), the modem automatically negotiates the best method of communication common to both negotiating modems. When error-control mode is used, data is transmitted asynchronously between the computer and the modem, while data is transmitted synchronously from modem to modem. An error-control protocol maintains data integrity between the connected modems. Operational Mode Selections &Q0 Select standard asynchronous operation. No data buffering, EC (error- control) or compression protocols are supported (direct mode). This mode must be selected when using the AT&Tn Test mode option. &Q1 Communicate in Synchronous Mode 1. Call is originated using asynchronous methods and modem switches to synchronous on-line state. DTR must be true for data transfer to begin. &Q2 Communicate in Synchronous Mode 2. Call is originated using synchronous methods automatically using the stored number dial command (ATDS=n) when on off-to-on transition of DTR is detected. &Q3 Communicate in Synchronous Mode 3. Call is originated by user using telephone connected to the same circuit as the modem. User then completes the call by switching to data mode and directing software to transition DTR from OFF to ON. &Q4 Hayes AutoSync mode. The modem places a call asynchronously then automatically switches to synchronous operation once the connection is fully established. &Q5* Select EC (error-control) mode of operation. Negotiation fallback options are controlled with S36. &Q6 Select asynchronous operation with automatic speed buffering (so- called "normal mode''). Local flow control required when the DTE and DCE speeds are not the same. &Q8 One-command selection of MNP operational mode. The result of AT&Q8 is the same as AT&Q5 with S48=128 and S36=5 or 7. S46 toggles compression on or off. &Q9 Conditional Data Compression: LAPM connection negotiates V.42bis if possible while an MNP connection does not negotiate MNP/5 data compression. &Rn RTS/CTS Options The AT&Rn command controls the manner in which the Request to Send (RTS) and Clear to Send (CTS) signals operate. AT&R0 (factory default) causes CTS to track RTS (observing the RTS-to-CTS delay interval determined by S26) while the modem is on-line. AT&R1 ignores RTS and asserts CTS when the modem is on-line. These options are only valid when the modem is in synchronous mode. &Sn Data Set Ready (DSR) Options The AT&Sn command controls the manner in which the DSR signal operates. AT&S0 (factory default) has the modem assert DSR at all times. The AT&S1 and AT&S2 commands will be acknowledged by the modem but will not affect the state of the DSR signal. DSR will remain asserted regardless of the AT&Sn setting. &Tn Test Mode Options The AT&Tn commands evaluate operation of the modem, its connection to the local terminal, and the communications link between the local modem and the remote modem. Using these tests, any failure due to a defective modem on either side of the communications link can be identified, as can faults attributable to the serial interface, computer, or software program. These commands work in conjunction with an optional test timer (S-Register S18) which specifies the number of seconds a given test is to be conducted. When S18 is at its default setting of 0, the AT&T0 command can be used to abort the test. Note: Ensure the modem is configured for AT&Q0 (unbuffered asynchronous mode) and set for 2400 bps before using these commands. AT&T0 ends any test in progress. The +++ escape sequence must be entered to return the modem to command mode prior to sending this command. AT&T1 initiates a local analog loopback test to verify the path between the local terminal and local modem. Characters received from the local terminal are looped back to the local terminal by the modem. AT&T2 is not used. AT&T3 initiates a local digital loopback test. Characters received from the remote modem are looped back to the remote modem by the local modem. This test verifies the working condition of the path from the remote modem, through the local modem, and back to the remote modem. AT&T4 allows the local modem to respond to a request from the remote modem for a remote digital loopback test. This is the factory default. AT&T5 prohibits the local modem from granting a request from the remote modem for a remote digital loopback test. AT&T6 initiates a remote digital loopback test. Characters received from the local terminal are transmitted to the remote modem and looped back from the remote modem to the local modem and terminal. This test verifies the working condition of the path between the local terminal and the remote modem. AT&T7 initiates a remote digital loopback self-test. This test works similarly to AT&T6 except that the local modem sends an alternating zeros and ones (0101) test pattern to the remote modem and continuously examines the validity of the returned data. The local modem increments an internal error counter each time an error is detected. At the end of the test, it returns a 3-digit error count to the local terminal. AT&T8 initiates a local analog loopback self-test. This test works similarly to AT&T7 except that the test pattern is checked in the local analog loopback mode (as in AT&T1). This allows a thorough testing of the local modem transmit and receive functions without an actual telephone line connection. AT&T19 determines whether or not the RS232C modem cable supports the RTS and CTS hardware handshake signals. If so, the modem responds with an OK, otherwise, it responds with an ERROR. Note: This test requires specialized software support for it to be conducted accurately. &Un Enable Trellis Code Modulation The AT&U or AT&U0 command enables trellis encoding of the data stream when V.32 modulation is active. This is the factory default. AT&U1 turns off trellis encoding. Modems that use Trellis Coded Modulation (TCM) can tolerate more than double the channel noise than those that use other modulation techniques. This makes for a more robust data transmission that is also less susceptible to impulse noise and other impairments on the telephone lines. Note that TCM is always unconditionally active for V.32bis connections at transmission speeds of 7200 bps and above. TCM can be activated at a data transmission speed of 9600 bps when using V.32 connections. &V View Stored Parameters The AT&V command allows you to view the contents of the Active Configuration Profile, Stored Profile 0, Stored Profile 1, and stored telephone numbers. &Wn Store User Profile You can store two configuration profiles in the modem memory. These profiles are referenced as Stored Profile 0 and 1. The active configuration settings are kept in the modem's RAM. The AT&Wn command allows you to save a subset of the configuration settings in a special area of nonvolatile memory. The variable n designates to which stored profile location the current configuration profile is saved. These settings are restored each time the modem is turned on, or they can be restored at any time by using the ATZn command. The AT&Yn command selects which stored profile will be loaded when the modem is turned on. &Xn Synchronous Transmit Clock Source The AT&Xn command determines how the DTE transmit clock is generated while the modem is in synchronous mode. AT&X0 (factory default) causes the modem to generate the transmit clock and apply it to pin 15. AT&X1 accepts a synchronous clock signal on pin 24 from the DTE and applies this clock to pin 15. AT&X2 causes the modem to derive the transmit clock from the receive carrier signal and apply it to pin 15. Note: Synchronous communication modes require the use of a fully-populated serial cable. Check with your cable supplier that the cable you are using is suitable for synchronous communication. &Yn Select Stored Profile on Power-Up The AT&Yn command, where n designates Stored Profile 0 or 1, sets the power-up default configuration profile. To power up using the configuration profile stored in memory location 0, the command is AT&Y0. To power up using the configuration profile stored in memory location 1, the command is AT&Y1. &Zi=n Store Telephone Numbers The AT&Zi=n command is used when you want to store a telephone number for later dialing using the ATDS=n (dial stored number) command. In this command, i represents a number between 0 and 3 designating one of four stored number locations. The variable n represents the string of dial digits and dial modifiers. The dial digits include 0 through 9 for both pulse and tone dialing. Tone dialing also includes the symbols A, B, C, D, #, and *. The dial modifiers discussed in this chapter include T P R W @ , ! and ;. To store a number for later redial, type the following: AT&Z1= T 1 800 555-1234 The modem responds with the result code OK. You have just stored T18005551234 in nonvolatile memory location 1 of your modem. This number can now be dialed by issuing: ATDS=1 To store the last number dialed for later redial, type the following: AT&Z2=L The modem responds with the result code OK. You have just stored the last number dialed in nonvolatile memory location 2 of your modem. This number can now be dialed by typing the command: ATDS=2 There is a 36-character limitation on the number of characters that can be stored in each string. This limit includes dial digits, dial symbols, and dial modifiers, but does not include spaces, hyphens, or the parentheses used as telephone number delimiters. If you type in more than 36 characters, the modem accepts only the first 36 characters and ignores the rest. $H View Help Information The AT$H command is used to display a multi-page summary of the commands supported by the modem. You can page forward through the command summary by pressing the space bar. Use [ESC] to exit from the help screen. AT% Commands %BAUD=n Clock Doubling This command enables or disables clock doubling at the UART. When clock doubling is enabled, the specified DTE or Baud Rate set in your communications software will be doubled by the modem's UART. Thus, a DTE speed of 115,200 bps will result in a 230,400 bps speed between the computer and the modem. %BAUD? Reports current clock doubler mode. (0 or 1). %BAUD=? Reports available clock doubler modes. (0 or 1). %BAUD=0 Disable clock doubler and use standard UART speed. %BAUD=1 Enable clock doubler and double specified UART speed. %C Data compression This command enables or disables data compression negotiation. The modem can only perform data compression when a LAPM or an MNP connection is established. %C0 Disables data compression. %C1 Enables MNP5 data compression negotiation. %C2 Enables V.42 bis data compression. %C3* Enables both V.42 bis and MNP5 data compression. The V.42 bis data compression employs a "string learning" algorithm in which a string of characters from the DTE (computer) is encoded as a fixed length code word. Two 2-kilobyte dictionaries are used to store the strings. These dictionaries are dynamically updated during normal operation. In MNP 5 data compression mode, the modem increases its throughput by compressing data into tokens before transmitting it to the remote modem, and by decompressing encoded received data before sending it to the DTE (computer). %CCIDn Caller ID function The caller ID function, which allows you to identify the telephone number from which an incoming call originated, is available in some areas of the United States and Canada. Use the %CCIDn command to enable this feature. If this service is available in your telephone area, the %CCIDn command options are: %CCID=0 Disable the Caller ID function (factory default). %CCID=1 Enable Caller ID function. If the modem detects a valid Caller ID incoming message between the first and second rings, the following information is displayed on your monitor screen: RING DATE = MMDD TIME = HHMM NMBR = nnn...nnn or O or P NAME = MESG = RING RING NOTE: In Short Form only Date, Time, and Number are displayed. MMDD = the current date where MM is the month (01 to 12) and DD is the day (01 to 31). HHMM = the time the signal was received where HH is the hour (00 to 23) and MM is the minute (00 to 59). nnn...nnn = the calling party's 10-digit telephone number. O = out of area. This usually indicates that either the sending or receiving party does not have the Caller ID facility available as part of their telephone service. P = private. This indicates that the sending party has disabled the Caller ID facility at the caller end for the duration of this call. NAME = , where is the subscription name. MESG = in printable ASCII hex numbers. This tag indicates a data item not listed above. The message is only possible for Multiple Message Format. %CCID=2 Enable the Caller ID function. If the modem detects a valid Caller ID incoming message between the first and second rings, information is displayed on your monitor screen as an ASCII representation of a hexadecimal bitstream. This bitstream represents the information described in %CCID=1, plus header and trailer information and a checksum calculation. The monitor display would be similar to the following: RING MESG = 060342424231 RING RING %CCID? Indicate the current setting of the %CCIDn command (0, 1, or 2). %CCID=? Indicate the range of valid %CCIDn command settings (0, 1, or 2). AT%DUMBn Dumb mode Your modem's intelligent functions, command recognition and result code display, can be turned off for certain applications. The suppression of these functions is the "Dumb Mode" option. Dumb mode can be used in such asynchronous, auto-answer applications as remote stock-exchange quotation displays, remote printer output, wire service news flashes, and any other application that requires non-attended or hands-off, remote output. Cmd. Description AT%DUMB0* Disable Dumb Mode AT%DUMB1 Enable Dumb Mode Note: Dumb mode can be disabled by typing AT%DUMB0 within 20 seconds of the modem being powered on. After 20 seconds, the modem will no longer respond to commands, in accordance with being configured as a dumb device. Dumb mode can be enabled at any time. %En Line quality monitor The AT%En command controls whether or not the modem will automatically monitor the line quality and request a retrain, or fall back (when line quality is insufficient) or fall forward (when line quality is sufficient). This command applies to dial-up lines only. %E0* Disable line quality monitor and auto-retrain. %E1 Enable line quality monitor and auto-retrain. %E2 Enable line quality monitor and fallback/fall forward. When AT%E2 is active, the modem monitors the line quality (EQM). When line quality is insufficient, the modem will initiate a retrain if EQM thresholds are exceeded. If the EQM is sufficient for at least one minute, the modem will initiate a rate re-negotiation to a higher speed. Speeds attempted during fallback/fall forward are those shown to be available in the rate sequences exchanged during the initial connection. Fallback/fall forward is available in error correction and normal modes, but not in direct mode or synchronous mode with external clocks. %L Line signal level Returns a value which indicates the received signal level. The value returned is a direct indication (DAA dependent) of the receive level at the MDP, not at the telephone line connector. For example, 009 = -9 dBm, 043 = -43 dBm, and so on. %Q Line signal quality Reports the line signal quality (DAA dependent). Returns the higher order byte of the EQM value. Based on the EQM value, retrain or fallback/fall forward may be initiated if enabled by AT%E1 or AT%E2. An example dialog would be: AT%Q 015 OK (If connected) ERROR (If not connected, or connected in 300 bps, V.23, or fax modes) AT\ Commands \An Maximum MNP block size The modem will operate an MNP error corrected link using a maximum block size controlled by the parameter supplied. \A0 64 characters. \A1* 128 characters. \A2 192 characters. \A3 256 characters. \Bn Transmit break to remote In non-error correction mode, this command will transmit a break signal to the remote modem. Specify the length of the break signal, in multiples of 100 ms, by setting n to an integer between 1 to 9, inclusive. If a number greater than 9 is entered, 9 is used. This command works in conjunction with the AT\Kn command. In error correction mode, the modem will signal a break through the active error correction protocol, giving no indication of the length. \Cn Auto-Reliable Buffer The AT\Cn command determines if data will be buffered during the 4 second window while the modem attempts to negotiate a reliable connection. The default AT\C0 disables this function. \C0* Disables auto-reliable buffer. \C1 Enables auto-reliable buffer. \C2 Disables auto-reliable buffer when connecting to a standard modem. \En Data Echo The AT\En command is similar to the ATE command. While ATE controls the local echo of characters in the command mode, AT\E controls the echo of characters in on-line mode. \E0 Disables echo. \E1* Enables echo. \Gn Modem-to-modem flow control In non-error correction mode, the modem enables or disables the generation or recognition of modem-to-modem XON/XOFF flow control according to the parameter supplied. The default is disabled (AT\G0). When enabled by the AT\G1 command, the modem supports XON/XOFF flow control with the remote modem to ensure data integrity. In error correction mode, the setting of modem-to-modem XON/XOFF flow control is ignored as flow control is accomplished within the error-correction protocol. The serial port flow control settings (AT&Kn), however, remain active during a reliable link. \G0* Disables modem-to-modem XON/XOFF flow control. \G1 Enables modem-to-modem XON/XOFF flow control. \Jn DTE auto rate adjustment This command controls whether the modem will adjust the DTE (computer-to- modem) speed to match the line speed when the connection is complete. The default setting, AT\J0, disables this function. \J0* Disable adjustment of DTE speed to match line speed. \J1 Enable adjustment of DTE speed to match line speed. \Kn BREAK control The modem can detect a BREAK signal from either the DTE or the remote modem. The AT\Kn command controls the response of the modem to a BREAK signal or the AT\Bn command, according to the parameter supplied. The response is different in three separate states: The first state is where the modem receives a break from the DTE when the modem is operating in data transfer mode: \K0 Enter on-line command mode, no break sent to the remote modem. \K1 Clear data buffers and send break to remote modem. \K2 Same as 0. \K3 Send break to remote modem immediately. \K4 Same as 0. \K5* Send break to remote modem in sequence with transmitted data. The second case is where the modem is in the on-line command state (waiting for AT commands) during a data connection, and the AT\Bn is received in order to send a break to the remote modem: \K0 Clear data buffers and send break to remote modem. \K1 Same as 0. \K2 Send break to remote modem immediately. \K3 Same as 2. \K4 Send break to remote modem in sequence with data. \K5* Same as 4. The third case is where a break is received from a remote modem during a non-error corrected connection: \K0 Clears data buffers and sends break to the DTE. \K1 Same as 0. \K2 Send a break immediately to DTE. \K3 Same as 2. \K4 Send a break in sequence with received data to DTE. \K5* Same as 4. Note that when S82 is modified, the modem converts the Hayes-specific value to the AT\Kn format and updates S40 to match. \Ln MNP block/stream mode select At connection time, this command controls the selection between block and stream modes of operation in the MNP error-correcting protocols. MNP 2-4 error correction is a data link protocol that uses error correction algorithms to ensure data integrity. \L0* Use stream mode for MNP connection. \L1 Use interactive block mode for MNP connection. This command will accept block mode but implement stream mode. In stream mode, the modem sends data frames in varying lengths depending on the amount of time between characters coming from the DTE (computer). In block mode, the modem sends data frames of 256 characters in length. special communication software must be used when using block mode. \Nn Operating mode The command controls the preferred error correcting mode to be negotiated in a subsequent data connection. \N0 Selects normal speed buffered mode (disables error-correction mode). Forces AT&Q6. \N1 Serial interface selected-selects direct mode and is equivalent to AT&M0 or AT&Q0 mode of operation. Forces AT&Q0. If parallel interface is selected, the command is the same as \N0. \N2 Selects reliable (error-correction) mode. The modem will first attempt a LAPM connection ad then an MNP connection. Failure to make a reliable connection results in the modem hanging up. Forces AT&Q5, S36=4, and S48=7. \N3 Selects auto reliable mode. This operates the same as \N2 except failure to make a reliable connection results in the modem falling back to the speed buffered normal mode Forces AT&Q5, S36=7, and S48=7. \N4 Selects LAPM error-correction mode. Failure to make an LAPM error- correction connection results in the modem hanging up. Forces AT&Q5, and S48=0. \N5 Selects MNP error-correction mode. Failure to make an MNP error- correction connection results in the modem hanging up. Forces AT&Q5, S36=4, and S48=128. \Qn Flow Control Options When the DTE (computer-to-modem) and DCE (modem-to-modem) data speeds are not the same, there is a requirement for data buffering and controlling the flow of data between modem and computer. The AT\Qn command controls how local flow control between DTE (your computer) and DCE (the local modem) is handled. \Q0* Disable local flow control. \Q1 Enable XON/XOFF software local flow control. \Q2 Enable CTS hardware local flow control. \Q3 Enable RTS/CTS hardware local flow control. \S On-Line Status The AT\S command allows you to view the contents of the active configuration profile. \Tn Inactivity Timer The AT\Tn command specifies the period of data inactivity while on-line after which the modem hangs up the telephone line. The valid range is 0 to 90 in one minute intervals. The default is 0 (zero) which disables the function. \Vn MNP Result Codes This command enables or disables reliable-link result codes. The format that the modem uses to return the result codes is controlled by the ATVn command. \V0 Disable MNP result codes. \V1* Enable MNP result codes. \Xn XON/XOFF Flow Control The AT\Xn command specifies the manner in which the modem will handle XON/XOFF characters in the data stream. The AT\X0 default, allows for local flow control only. When configured for pass-through flow control, the modem will pass the control codes on to the remote system. \X0* Local XON/XOFF flow control only. \X1 Local and pass-through XON/XOFF flow control. 4 CONFIGURATION, PROTOCOLS AND GENERAL CONSIDERATIONS Your modem was configured at the factory with certain sets of default parameters. Some of these defaults may need to be changed to conform to your specific requirements or those of your communications software. Practical Peripherals modems use a switchless technology to alter and store your configuration values. You can turn these solid-state switches ON or OFF with software commands from your computer. The altered configuration can be stored in the modem by issuing a simple keyboard command. Note: Unless a command is listed in the Operating Manual provided with your modem, it is not supported by your modem, although it appears in this document. Configuration Profiles A configuration profile is a set of modem operating parameters. The active set of parameters, called the active configuration profile (ACP), resides in the modem's random access memory (RAM) while the modem is switched on. In addition to the active configuration profile that is stored in RAM, the modem has the ability to store two customized configuration profiles in its nonvolatile memory. The factory default configuration profiles are located in the modem's read-only memory (ROM). Active configuration profile The values contained in the ACP determine just how the modem operates. The ACP is loaded into the modem's RAM when the unit is switched on. Some of these values are loaded from ROM; others are loaded from nonvolatile memory. Although all of the values can be changed in RAM, only that subset of values loaded from nonvolatile memory can be altered and stored for future recall. S-Register values in the following list are used when the modem is switched on. These values are part of the factory default settings and are stored in ROM. Although the values can be changed temporarily, the changes you make cannot be stored in nonvolatile memory. The default ROM values, therefore, are effective again when the modem is next switched on or reset. S1-Ring Count (00) S3-Carriage Return Character (13) S4-Linefeed Character (10) S5-Backspace Character (08) Storing configuration profiles The modem can store two sets of configuration parameters in nonvolatile memory. The values stored are those of the ACP in RAM. The ACP set of values are written to memory with the AT&Wn command, where n is location number 0 or 1. Make any desired changes to the ACP before issuing the command to write the values to nonvolatile memory. Establishing the power-up profile When the modem is switched on, the active configuration profile is read into the modem's RAM. The setting of the AT&Yn command determines which of the two stored profiles the modem uses as the active profile. AT&Y0 makes Stored Profile 0 the ACP. AT&Y1 makes Stored Profile 1 the ACP. Factory configuration profiles Factory configuration values are stored in ROM. If you want the modem to be reset to the factory defaults you have chosen as your basic configuration, you can type in an AT&Fn command, where n=0 to 3. See The place to start, later in this chapter. The AT&Fn command copies your chosen factory default configuration from ROM to the ACP. If you want your chosen factory profile to be the ACP when the modem is next switched on, use the AT&Fn&Y&W command. This writes the factory parameters into configuration location 0 in nonvolatile memory, and sets configuration location 0 as the default power-up configuration. Viewing the configuration profiles The AT&V command displays the current values for the active profile, stored profile 0, stored profile 1, and stored telephone numbers. Modem Configuration Guidelines Every PPI modem is capable of an extensive array of configuration options. These options allow you to tailor the modem's operation to suit the needs of a wide variety of communications software and telecommunications applications. The place to start The factory defaults are a fixed and known set of modem parameters. The factory defaults enable the modem to automatically negotiate a connection with another modem. The set you choose to implement depends on the type of installation to which your modem is connected and how you prefer to operate your data communications applications. To set the modem to your choice of factory defaults, type one of the following: AT&F&W This command line loads the Hayes-compatible set of factory defaults into your modem and is suitable for use with an asynchronous ASCII data terminal. AT&F1&W This set of factory defaults, used with most communication packages, suits most IBM PC, XT, AT or AT-compatible environments. AT&F2&W This set of factory defaults suits the Apple Macintosh environment using the software handshake method of connection. AT&F3&W This set of factory defaults suits the Apple Macintosh environment implementing the recommended hardware handshake method of connection. The &W command at the end of each of the above command lines writes the complete active configuration profile to the nonvolatile memory of the modem. This enables you to recall your configuration with either a power cycle (turning the modem off and then back on again) or with the ATZ reset command. S-Register Configuration Active configuration settings are stored in configuration S-Registers designated S0 through S255. Some modems contain less than 256 S-Registers. Many S-Registers are reserved for internal use by the modem's firmware, while others in the sequence are set aside for future enhancements and are not implemented at this time. Each S-Register contains eight bits. S-Registers can be directly read from or written to using the ATSn? and ATSn= commands, respectively. An S-Register subset is read from the modem's nonvolatile memory each time the modem is switched on or reset. The factory S-Register configuration settings are permanently stored in ROM. These parameters can be loaded into the active configuration area by issuing the AT&Fn command. A summary of the S-Registers implemented in your modem can be found in Appendix A of the manual included with your modem. A more complete description of all available S-Registers, their factory settings, alternatives, and other details can be found in Chapter 2. Modifying the S-Registers The basic format of the command to modify an S-Register is: ATSn=x In this command, n indicates the S-Register number and x indicates the value to be written. For example: ATS0=2 The S-Register S0 changes from its current value to a new setting of 2. This means your modem will automatically answer incoming calls after the second ring. When the command has been successfully completed, the modem responds by displaying OK on your monitor screen. Reading an S-Register The format of the command to read an S-Register is: ATSn? In this command, n indicates the number of the S-Register to be read. For a single S-Register read request, type: ATS0? The instruction has been given to read S-Register S0. The response displayed on your monitor screen is: 002 OK The current value of that S-Register is 2 (rings). The modem replies with that number in a three-digit format and adds the OK to acknowledge that the command has been completed and the modem is waiting for further instructions. For a multiple S-Register read request, type: ATS0?S7? The request has been made to read both S-Registers S0 and S7. The response displayed on your monitor screen is: 002 050 OK The modem has responded with the contents of those two S-Registers, each in a three-digit format. Completion of the command is acknowledged with OK. Modulation Protocols All information in a digital computer is encoded as an arrangement of ones and zeros called binary digits (bits). The function of a modulator/demodulator (modem) is to convert streams of these bits from digital signals into analog signals (sound) which can be transmitted over standard telephone lines. The receiving modem reconstitutes the analog signals into a reproduction of the original, digital bit stream for processing by the receiving computer. The specific techniques used to encode the bit stream into analog signals are called modulation protocols. As modem technology has developed, new modulation techniques have evolved to allow more information to be transmitted securely within the limited bandwidth of the voice telephone system. Modulation protocols define the exact method of encoding the data, and dictate the data transfer speed. For example, the Bell 103 protocol describes how to send 300 bits per second (bps) by way of the telephone lines, using the frequency shift keying (FSK) method of modulation. ITU-T V.22 defines the international standard for 1200 bps data transfers on voice telephone lines, using a completely different modulation method involving the phasing of the signals. The Bell 212A protocol defines the 1200 bps standard of data transmission used in the U.S., and differs slightly from the ITU-T V.22 protocol. The international standard for 2400 bps data transfer over telephone lines is the ITU-T recommendation V.22bis which uses still another modulation method called quadrature amplitude modulation (QAM). ITU-T V.32 is the international protocol for full-duplex 9600 bps data transfers. Modulation protocols should not be confused with such error-control protocols as ITU-T V.42 or MNP Class 2-4, data-compression protocols such as ITU-T V.42bis or MNP Class 5, or file-transfer protocols such as XMODEM or YMODEM. Modulation protocols deal with methods used to encode digital data into analog signals and the arrangement of tones that modems exchange while negotiating a connection. File-Transfer Protocols Your modem cannot tell the difference between data being entered from the keyboard or data streaming from the hard disk. The modem does not understand the concept of a file. It works only with bytes, bit streams, timing and tones. Although the modem does not understand the concept of the file, the modem is the device which makes file transfers by way of the telephone possible. Your modem relies on your communications software to manage such file details as the filename, the size of the file, and file content validity. The software modules that handle these details are called file-transfer protocols. XMODEM is perhaps the best known error-checking, binary file-transfer protocol. It is a block-oriented protocol that organizes a file into 128-byte blocks. A checksum or cyclic redundancy check (CRC) is performed on each data block and the result is transmitted with the data block. As each block is received, the checksum or CRC value is recalculated. Each valid block is acknowledged with an ACK. If the checksums do not agree, the receiver requests retransmission of the defective block by returning a NAK. Conceptually, this is similar to the task performed in hardware by the modem's error-control protocols. XMODEM, however, is a software-based, file-oriented protocol that functions on a computer-to-computer basis. The LAPM or MNP reliable link on the other hand is a hardware-based, data-frame-oriented protocol that functions on a modem-to-modem basis. This distinction is very important. Although the hardware reliable link produces 100-percent error-free data exchanges during an interactive ASCII session, a file-transfer protocol is still required for binary file transfers. Since the modem does not understand the concept of a file, a file-transfer protocol is needed to handle such details as determining when the file starts, the name and size of the file. Modem Modes The modem is always in one of two primary modes. When first switched on, the modem starts up in command mode. In this mode, the command processor is constantly checking to see if you have typed a valid AT command. When it receives a valid command, it executes that command for you. While your modem is in this mode, you can instruct it to answer the telephone, change an S-Register value, hang up or dial the telephone, and perform any number of other command functions. The other mode is on-line mode. In this second mode, your modem is transmitting all of the data it receives from your computer or terminal along the telephone line to the remote modem. Your modem is constantly checking the state of the Data Carrier Detect (DCD) and Data Terminal Ready (DTR) signals depending on configuration. It is also watching the local data stream for the escape sequence. The default escape sequence is +++. When the proper escape sequence or a change in the state of the DCD or DTR signal occurs, the modem returns to command mode where it waits for the next AT command. Asynchronous Transmissions Most communications between PC's are asynchronous. Asynchronous transmissions send data between the modems as characters. Data is transmitted as character bits framed by start, stop, and parity bits to mark the beginning and end of character units. The use of parity bits is optional, depending on the character format selected. Valid Modem Character Formats Start Bits Data Bits Parity Stop Bit(s) 1 7 even or odd 1 1 7 none 2 1 7 mark or space 1 1 8 none 1 Synchronous Transmissions Synchronous communication is a specialized form of data transmission and usually requires specific hardware and software combinations. When operating in a synchronous mode, the modems send bits across the link in uniform blocks of time, therefore, start and stop bits are not required. Since synchronous communication is timing sensitive and requires data to be sent at each clock tick, special protocols are used to handle idle sequences. Serial Interface Pin Assignments Pin Description Signal Direction 1 Frame Ground 2 TXD (Transmit Data) To modem 3 RXD (Receive Data) From modem 4 RTS (Request to Send) To modem 5 CTS (Clear to Send) From modem 6 DSR (Data Set Ready) From modem 7 GND (Signal Ground) 8 DCD (Data Carrier Detect) From modem 12 SCF (HS -- Secondary RLSD) From modem 15 TXC (Synchronous transmit clock) From modem 17 RXC (Synchronous transmit clock) From modem 20 DTR (Data Terminal Ready) To modem 22 RI (Ring Indicator) From modem 23 CH/CI (HS - Data Rate Signal Select) Tied to pin 12 24 DA (Synchronous transmit clock source) To modem Note: Normal, asynchronous operation of this modem requires a shielded, straight-through serial cable that supports pins 1 through 8 and 20. Pins 12 and 22 could be required for operation with some BBS software. Synchronous operation requires a fully-populated serial cable. RS-232 Signal Definitions This section provides definitions of the signals used for modem operation. Protective Ground (Pin 1) This signal is connected to the equipment frame. The ground pin is bonded to the computer's housing through the bus for internal modems. Transmit Data (Pin 2) This pin passes data from the DTE to the DCE device. This is the circuit that carries the data from the attached computer or terminal to the modem for transmission across the telephone lines. Receive Data (Pin 3) This pin passes data from the DCE to the DTE. This circuit carries the data from the modem to the attached computer or terminal. Request to Send (Pin 4) This circuit indicates whether the attached DTE is ready to receive data from the modem. Clear to Send (Pin 5) This circuit indicates whether the modem is ready to receive data from the DTE. Data Set Ready (Pin 6) This signal indicates whether the modem is connected to a communication channel and is ready to initiate data transmission. Signal Ground (Pin 7) This circuit establishes a common ground reference potential for all signal circuits. Data Carrier Detect (Pin 8) This signal indicates whether the receiver section of the modem is or is not accepting transmitted data. HS-Secondary RLSD (Pin 12) This signal indicates the current line speed. Transmitter Clock (Pin 15) This signal synchronizes the modem with the attached computer or terminal receiver when the modem is in synchronous mode. Receive Clock (Pin 17) This signal synchronizes the modem with the attached computer or terminal transmitter when the modem is in synchronous mode. Data Terminal Ready (Pin 20) This signal indicates to the DCE that the local computer is ready to receive data. It may also be used for call termination. Ring Indicator (Pin 22) This circuit carries signal information to indicate the modem is receiving an incomming call. Transmitter Clock (Pin 24) This circuit provides the modem with transmit signal element timing information. This signal pertains to synchronous modes only. Hayes AutoSync Hayes AutoSync mode, AT&Q4, is an alternative method for achieving synchronous communication from a personal computer. It allows the user to communicate with synchronous computers from most asynchronous serial computer ports. Use of Hayes AutoSync requires software which incorporates the Hayes Synchronous Interface (HSI) software. With Hayes AutoSync the initial call is made asynchronously. Upon connection, the modem switches into a special mode that makes the asynchronous port appear synchronous. Automatic Speed Buffering (ASB) Automatic Speed Buffering (ASB) is useful for computers and communication programs that do not automatically adjust to changing transmission speeds. ASB enables computer equipment to send and receive data to and from the attached modem at one particular transmission speed, regardless of the speed of the modem-to-modem connection. ASB buffers data temporarily, using local flow-control to parcel it from the computer as the modem is ready to receive it. The modem must be set with the AT&Kn command to use the appropriate flow-control method. When using ASB, the modem signals the local computer when to start and stop sending data, depending on how full the modem's buffer is. Macintosh Hardware Handshake Cable A hardware handshake cable allows the Macintosh to assert both the DTR and RTS handshaking signals with its HSKo (handshake-out) control line. The HSKi (handshake-in) control line allows the computer to monitor the Clear to Send (CTS) signal from the modem. Mac Pin and Function DB25 (RS232) Pin and Function ----------------------- ----------------------------- Pin 5 (Receive Data) Pin 3 (Receive Data) Pin 3 (Transmit Data) Pin 2 (Transmit Data) Pins 4 & 8 (Ground) Pin 7 (Ground) Pin 2 (Handshake In) Pin 5 (Clear to Send) Pin 1 (Handshake Out) Pins 4 and 20 (Ready to Send & Data Terminal Ready) Since DTR is tied to RTS, you must have the modem set to ignore any state change of DTR, otherwise an RTS flow control change would cause the modem to hang up the telephone line. With this cable use: AT&F3S95=44&W This command stores the required parameters in the modem's nonvolatile memory. If you wish to use this command in your software modem initialization string, do not use the &W write command. Macintosh Software Handshake Cable In this case, HSKo is used to control only the DTR signal to the modem while HSKi monitors the DCD signal from the modem. Data is transmitted and received as described for the hardware handshake cable. Because the functions assigned to HSKo and HSKi are different with this cable, the modem parameters must be different as well. Mac Pin and Function DB25 (RS232) Pin and Function ----------------------- ----------------------------- Pin 5 (Receive Data) Pin 3 (Receive Data) Pin 3 (Transmit Data) Pin 2 (Transmit Data) Pins 4 & 8 (Ground) Pin 7 (Ground) Pin 2 (Handshake In) Pin 8 (Carrier Detect) Pin 1 (Handshake Out) Pin 20 (Data Terminal Ready) For this cable use: AT&F2S95=44&W As noted previously, this form of the command is intended to be stored in the modem's memory. If you wish to use this string as your program's modem initialization string, omit the &W. 5 High-Speed Considerations This chapter introduces you to some of the essential concepts that will help you understand the power and flexibility of your high-speed modem. The proper modem configuration parameters for an error-control (EC) modem are closely connected to the setup of the communications program you are using. The modem settings and the program settings must be coordinated in order to form a successful partnership. Your communications software should support both hardware and software flow- control options, and should have the ability to enable and disable these options separately. Generally, with an EC modem, you will want your communications program set with hardware flow control enabled and software flow control disabled. The modem's default flow-control parameter (AT&K3) is for local hardware Request to Send/Clear to Send (RTS/CTS) flow control to be enabled. It is important that the flow-control options of the modem and the software are in agreement. If they are not, you are certain to have problems with file transfers. If you can download files but have consistent failures when trying to upload files, this almost always indicates a flow-control problem. Mid- file lockups, with binary files being transferred using the XMODEM protocol, are often due to having software flow control enabled in the communications software. This is one reason why hardware flow control is usually recommended. Whenever your computer is communicating with the modem at one speed and the data speed across the telephone line to the other modem is different, you must have some form of local flow control enabled. If not, you will ultimately suffer a data loss. Since speed differences between the serial port and the modem link are normal with an EC modem, and your modem defaults to having hardware flow control (RTS/CTS) enabled, you will need this feature enabled in your communications program as well. If it is only enabled in the modem parameters and not in your software, or if you are using a program which does not support flow- control options, you cannot obtain the full benefits from your modem. The hardware error-control protocol handles data flow control between the two modems once a V.42 or MNP connection is established. Local flow control between your computer and your local modem, however, is a cooperative process involving both the setting of the modem parameters and the setup in your communications program. Trellis Coded Modulation Trellis Coded Modulation (TCM) encoding is a forward, error-correcting technique that allows a modem to more readily recover data corrupted by noise and other transmission impairments on the telephone line. Trellis encoding allows error detection and correction without retransmission of the data. This is different to and separate from the error-control methods of the V.42 LAPM and MNP protocols. Trellis encoding is available when the modem is operating in the ITU-T V.32 or V.32bis mode and connected to another V.32 or V.32bis modem. In the case of V.32bis, TCM is unconditionally active at 7200 bps and above and cannot be disabled. In the case of V.32, TCM can be activated only at 9600 bps. The factory default is for TCM to be enabled. It can be disabled with the AT&U1 command. Error-Control Protocols Practical Peripherals error-correcting (EC) modems support ITU-T recommendation V.42 LAPM and alternate MNP protocols. EC modems obtain error-free data transfers by first detecting received data that does not match the transmitted data, and then requesting that the data be resent. Data is transmitted in the form of information packets that contain both the data and information about the data. The procedure is similar to that used by standard software file-transfer protocols to ensure data integrity, except, in this case, the procedure is performed in the modem hardware. The sending modem performs a complex mathematical computation on the data content. The result of this calculation is attached to the data packet as an error-control value before it is transmitted. The receiving modem repeats the error-control calculation on the received data packet. If the result of the calculation by the receiving modem is equal to the error-control value contained in the packet, the packet is accepted as containing correct data. If the error-control values differ, the receiving modem requests that the packet be resent. This process is repeated until either the received packet is determined to be correct or the connection is terminated due to excessive errors. The V.42 error-control mode is the factory default (AT&Q5) for all EC modems. The modem automatically negotiates with the remote modem to establish a link access procedure for modems (LAPM) connection. The default parameter (S36=7) also allows the modem to fall back to a Microcom Networking Protocol (MNP) connection or an asynchronous connection based on the remote modem's response to the negotiation. Data-Compression Protocols Practical Peripherals data-compression modems support two different data- compression protocols-ITU-T recommendation V.42bis and MNP Class 5. The requirement that an EC protocol connection exists before data compression can be attempted is common to both. You can have an EC connection without data compression, but you cannot have data compression without underlying EC protocol support. V.42bis requires a LAPM connection while MNP Class 5 requires an MNP Class 2-4 connection. Data compression is not possible in standard, non-buffered asynchronous mode (AT&Q0) or asynchronous automatic speed buffering (ASB) mode (AT&Q6). Data compression does not alter the number of signal transitions or the number of data bits transmitted during a given period of time. By removing repetitive bits in the data, however, the compression algorithm increases the information content of the bit stream. Thus, the effective information throughput is increased in a manner somewhat similar to a stenographer taking notes in shorthand. The theoretical compression ratio for V.42bis is 4:1; while 2:1 is the maximum for MNP Class 5. The actual compression rate obtainable with either protocol is data dependent. ASCII text and spreadsheet files compress to the greatest degree. Binary files such as .COM or .EXE files allow significantly less compression. Generally, files which have already been compressed, such as .ARC or .ZIP files, do not allow any further data compression. With MNP, it is generally better to disable data compression if you are going to transfer already-compressed files. The V.42bis algorithm can recognize a compressed file and does not attempt any additional compression. Compression is either enabled or disabled with the value of S-Register S46. The default value is 2 (enabled). The appropriate compression function is enabled in accordance with the EC protocol negotiated during the connection handshaking sequence. If the remote modem does not support a common compression protocol or has it disabled, there will be no data compression regardless of the setting of S46 in the local modem. Your modem has a conditional compression capability which is enabled with the AT&Q9 command. With AT&Q9 active, the modem disables data compression if the connection is an MNP connection and enables data compression if the connection is a V.42 LAPM connection. The AT&Qn command default setting is AT&Q5. Maximum Throughput Maximum throughput is achieved when the file being transferred is an ASCII text file, the local serial port data-transmission rate is higher than that of the modem port, and data compression is enabled. Note, however, that using MNP Class 5 data compression on a file that is already compressed can be counterproductive. When transferring .ARC or .ZIP files, it is suggested that MNP Class 5 data compression be turned off. Disabling data compression for these types of files is not necessary when using V.42bis because the protocol algorithm senses an incompressible file and automatically suspends compression. The use of the AT&Q9 conditional compression setting automatically avoids MNP Class 5 on MNP connections and enables V.42bis on LAPM connections. Generally, the most efficient file-transfer operations are achieved when the EC modem does the error checking in hardware, and the file-transfer protocol does not duplicate this effort. The YMODEM-G file-transfer protocol provides this level of service. This protocol was written for use with high-speed, error-control modems. This protocol does not provide any error-detection or recovery capability. Support of file-transfer protocols tailored to the needs of an error-control modem should be a consideration when selecting a communications package for use with your modem. Note, however, that the combination of an EC modem and reliable connection only provides data integrity between the two modems. Any errors that occur beyond the modem-to-modem link will go undetected. Fortunately, such errors are extremely rare. Although ZMODEM is a software error-control protocol which entails some of the error-checking redundancy mentioned earlier, practical experience indicates the throughput penalty is small. The advantage of ZMODEM's ability to resume an interrupted file transfer makes any small speed penalty a minor consideration. The resume capability along with the robust nature of this file-transfer protocol makes it an excellent choice for use with both standard or EC modems. Data Buffering and Flow Control With EC/DC modems, whenever the speed of data between the computer and serial port of the modem is different from the speed of data flowing between the connected modems, there must be some form of data flow control. Without flow control and data buffers, sustaining speed differentials would result in lost data and inefficient operation. To exploit the full data-transfer capability of a telephone connection between two modems, there must be a constant and steady supply of data ready to be encoded and transmitted on the telephone line. If the flow of data on the telephone line stopped while the computer was reading or writing data or the modem was preparing packets, the throughput rate would suffer. The general practice with EC modems, therefore, is to set the computer-to- modem data rate faster than the telephone line rate, and buffer the speed differential through the use of memory built into the modem. If you are putting data into a buffer faster than it is being removed, it is easy to see that at some point the buffer will be unable to accept more data until some is removed. For example, if an EC connection is established between two modems with a line speed of 9600 bps and the local computer is supplying data to the local modem at 19,200 bps, the buffer quickly fills and overflows unless there is a method to tell the computer to stop sending data. This is the purpose of local flow control. The modem can signal the computer to stop sending data to the input buffer, or the computer can tell the modem to stop sending data while it takes care of internal processing, such as writing to disk. Local flow control works in both directions between the computer and modem. For easier understanding, and since it works essentially in the same manner in either direction, we will examine it from the computer-to-modem viewpoint. With data flowing into the buffer at double the rate that it is flowing between the two modems over the telephone line, the buffer quickly fills. Before the buffer is completely full, the modem signals the computer to stop sending data. When the buffer is again ready to accept new data, the modem alerts the computer it is ready to receive data again. Although the data from computer to modem is moving at a higher rate than data on the telephone line, it is also doing so in a stop-and-go pattern. The data on the telephone line, however, maintains a steady flow. Your modem contains random access memory (RAM) which is used to provide data buffers. These buffers are an essential part of the scheme allowing error control and data compression as well as automatic speed buffering (ASB) in the non-protocol modes. Like most other EC modems, your modem supports both hardware Request to Send/ Clear to Send (RTS/CTS) local flow control (AT&K3), which is the factory default, and software (XON/XOFF) local flow control (AT&K4). Hardware flow control (AT&K3) is achieved through the raising and lowering of voltage levels on the RTS and CTS signal lines at the RS232C serial interface between the modem and the computer. Hardware flow control is generally preferred over software flow control on high-speed modems. Software flow control (AT&K4) is accomplished by embedding control characters in the data stream. XON and XOFF are the most commonly-used control characters for this purpose. These control characters are also known as Control-Q and Control-S, or DC1 (ASCII 17) and DC3 (ASCII 19), respectively. The use of XON/XOFF flow control can create problems under certain circumstances. These problems can arise from several sources. The most common source is an attempted transfer of a binary file that contains the DC3 (Control-S) character as a legitimate part of the data, and some element in the link interprets this as a flow-control character and stops transmission of data. The file-transfer protocol then times out and the file transfer is aborted. If the transfer of a given file is successful using the Kermit file-transfer protocol, and fails using XMODEM, most often the failure can be traced to the use of software flow control. In addition to the need for local flow control, when there are speed differences between the local Data Terminal Equipment (DTE) and the local Data Communications Equipment (DCE), there can be circumstances under which you may need to exercise both local and end-to-end flow control. One circumstance could be where the modem is directly connected to a serial printer that operates slower than the line data speed. Such a situation would demand both local and end-to-end flow control. This is the purpose of the AT&K6 and AT&K7 commands. These commands allow the passage of the XON and XOFF characters to and from the remote modem. Unless you have a very specialized application, you will probably never have the need for the functions enabled by AT&K6 or AT&K7. Generally, end-to-end flow control is handled automatically as part of the hardware error-control connection protocol or your software file-transfer protocol. Sample Modem Configurations Although your modem supports a large number of configuration options providing great flexibility for you to fine-tune the modem parameters to suit your needs, getting started with the modem is easy. For automatic full-feature negotiation, type: AT&Fn [Enter] where n=0 to 3, depending on the specific set of factory defaults you have chosen for your particular hardware configuration and communications application. See The place to start, earlier in this chapter. If you want to force the modem to forgo all error-control protocols, type in the following command line: AT&Fn&Q0&K0 [Enter] This command forces the modem to negotiate a standard, non-error-control link with the remote modem and disables local flow control. Remember, this mode does not allow speed differences between the computer and the modem-to-modem data rate. It is an unbuffered mode, so you must set your communications software to the same speed as the data link with the remote modem. For example, if you were calling a 2400 bps modem, you would set your communications program for 2400 bps. If you wanted a non-error-control connection with a 2400 bps modem, but did not want to change your local communications program speed from its setting of 9600 bps, you could use the automatic speed buffering (ASB) mode. For this type: AT&Fn&Q6 [Enter] To force an MNP connection with data compression turned off, type: AT&Fn&Q8S46=0 [Enter] If you use the modem to call multiple bulletin board systems where one system has a V.42 modem and another has an MNP modem, you may want to use the following initialization: AT&Fn&Q9S95=44 [Enter] The use of the AT&Q9 command makes the compression function conditional upon the protocol supported by the remote modem. If the remote modem supports MNP, the modem negotiates an MNP Class 4 connection without compression. If the remote modem supports V.42 LAPM and V.42bis, the modem negotiates a LAPM connection with V.42bis data compression. The S95=44 enables extended connection result messages. Universal Asynchronous Receiver/Transmitter (UART) A UART is a Universal Asynchronous Receiver/Transmitter integrated circuit chip onboard your internal modem or your serial I/O card. The job of a UART is to convert the stream of bits from the computer bus to bytes of data coming out of the serial port. With external modems it is therefore part of the computer. The 16550 UART contains a buffer that helps to prevent data from overrunning the serial port during high speed communication. On some serial cards the UART is socketed and can be replaced. In other cases the chip is soldered or part of a single VLSI chip on the card, or the serial port may be integrated with the computer's system board. In these cases, a new serial card must be used to gain the advantages of a buffered UART. A buffered UART is not essential with a computer using DOS-based applications, but if you use Windows or other multi-tasking software it becomes much more important. If your system is overloaded by many tasks (TSR's) or has a slow processor, then there may be a need for the 16550 UART at high speeds (above 9600bps). The 16550 utilizes onboard buffers that prevent the CPU from missing data when the CPU is over-loaded. In general, the way to find out if you need the 16550 UART is to look for "missing characters" or many CRC errors during file transfer at high port speed. High port speed is any speed above 9600bps. In other words if there are missing characters at 38400 port speed and lowering the port speed to 9600bps resolves the problem, then you need the 16550 UART. This is true about all different types of CPU's and systems. When a character arrives in the UART (the chip which changes the received bit stream into a 'byte of data') the UART issues an interrupt to the CPU in the host computer. The computer then stops doing what it was doing, shoves all of its environment on the stack, calls the ISR (interrupt service routine) and goes to pick up the character in the UART. Then it places that character in the communications application receive buffer, pops the stack, and returns to the task it was doing before the interrupt. This process repeats itself for each and every received character. If you install a number of TSRs or a disk cache program or anything which might suspend interrupts or cause any delays in the CPU responding to the UART interrupts, then you run into the 'dropped character' situation. What happens is that while the CPU is taking care of business with the first character, a second character arrives, then a third. But, the third character overwrites the second character before the ISR has had a chance to get the second character. The result is that one of the characters is missing. ProClass High Speed Serial Port (PC-HSSP) The ProClass High Speed Serial Port (PC-HSSP) is a communications accelerator designed for use with the Microsoft Windows environment. It provides automatic flow control and two 1024-byte buffers to prevent data loss at transmission speeds up to 921,600 bps. The PC-HSSP card is fully backward compatible with conventional 16450 and 16550 serial ports. Practical Peripherals provides serial communications drivers which fully support ESI and PC-HSSP's DMA Enhanced Mode for Windows 3.0 and 3.1. With these drivers installed, all applications (including DOS applications under this environment) gain the full advantage of DMA transfers and automatic flow control with no special programming required; the serial drivers provide the same API (application programming interface) as the standard Microsoft and IBM serial drivers, with the details of the PC-HSSP DMA operation hidden inside. While the standard Windows serial driver can suffer data loss at speeds as low as 9,600 bps, with PC-HSSP and the PC-HSSP driver for Windows, full-duplex communications as fast as 57,600 bps can be accomplished with complete data integrity and increased availability of CPU processing power to other applications. The implementation of block mode transfers in the Windows 3.1 kernel and the use of this mode by the PC-HSSP Driver for Windows 3.1 considerably improves performance of the driver over the standard Windows serial driver. The driver supports both PC-HSSP ports and standard serial ports, for systems which support a combination of both. Appendix A Glossary algorithm. A formula or procedure that employs various methods defining how data is to be used to give a prescribed result. analog signal. Signals that can vary over a continuous range (the way the human voice varies over conventional telephone lines.) Analog circuitry is more subject to distortion and noise, but it is more capable of handling complex signals than are digital signals, which can have only discrete values. ARQ. Automatic ReQuest for retransmission. A type of communications link where the receiver asks the transmitter to re-send a block of data when errors are detected. ANSI. A non-profit, private industry association that governs most USA standards setting agencies. ASCII. American Standard Code for Information Interchange. ASCII is a subset of the ANSI character set. The standard ASCII character set consists of 128 decimal numbers (0-127) for letters of the alphabet, numerals, punctuation marks and common special characters. The extended ASCII character set extends to 255 characters and contains special mathematical, graphics and foreign characters. asynchronous communication. A method of transmission in which data is synchronized with a start bit at the beginning of each character set and one or two stop bits follow each character set. Bell standards. Refers to the domestic modulation protocol standards developed by the former AT&T Bell Systems such as Bell 103 (300 bps transmission) and Bell 212A (1200 bps transmission). bit-mapped registers. An S-register that contains multiple bit oriented values. Example: the value of S22 is the sum of the bit values that you select (bits 0-1: speaker volume/value: 0-3;bits 2-3: speaker control/value: 0-3;bits 4-6: limit result codes/value: 0,4-6,7). blind dialing. An automated process whereby the modem goes off-hook and dials without waiting for a dial tone. This is prohibited in many countries. block transfer control. Determines whether the modem uses block or stream mode during an MNP connection. In stream mode, MNP sends data frames in varying length. Block mode sends fixed data frames of 256 characters and is selected with the MNP-based \L command. break handling. Determines how the modem responds when a break signal is received from either the DTE (Data Terminal Equipment or computer/terminal) or the remote modem. This is controlled by the MNP-based AT extended command \K. A break signal is represented on the communications line by a steady space signal for a significant length of time. Break signals can be activated from the keyboard by pressing the break key or the control (Ctrl) and C keys. CCITT. Consultative Committee for International Telephone and Telegraph. This advisory organization is part of the International Telecommunication Union (ITU), which is an agency of the United Nations that recommends specifications for communications equipment. This body is now known as ITU-T. command mode. The modem is in command mode when it is turned on or reset, when it loses its connection to a remote modem, or when escape characters (+++) are typed. To transmit data, the modem must be in data mode. communications protocol. A set of procedures that controls how a data communications network operates. DCD. Data Carrier Detect. Indicates to the terminal device that the modem is receiving a valid carrier signal from a remote modem. The carrier is a tone at a specified frequency. DCE. Data Communications Equipment. The local and/or remote modem. A DCE is usually connected to a DTE. DTE. Data Terminal Equipment. The computer or terminal, either local ( yours) or remote (the one you are communicating with). A DTE is usually connected to a DCE. DTR. Data Terminal Ready. The computer issues this signal to the attached modem indicating that it is ready to receive data. data compression. A technique that examines transmitted data for redundancy and replaces strings (groups) of characters with special codes that the receiving modem interprets and restores to its original form. Transmission of compressed data results in shorter connect times and hence cost savings for connect charges. Data compression is sometimes called source encoding. data mode. The modem is in the data mode when a connection has been established with a remote modem and sends a connect response confirming connection. User data can then be transmitted or received. dial modifier. Dial modifiers are special characters appended to the ATD command that instruct the modem how to place a call. digital signal. A discrete signal that is limited to one of several (usually only two) discrete levels, in contrast to analog signals that can take a continuous range of levels. error detection and correction. The transmitting modem attaches a special pattern (called a frame check sequence) calculated according to a prescribed algorithm from user-defined data to the end of a block of data. The receiving modem performs the same algorithm and compares it to the one with the transmitted data. If these match, then the block of data has been received correctly. If not, the block of data is re-transmitted until no errors are detected. escape sequence. Also referred to as the escape command. This special command is entered as three plus symbols (+++) and places the modem in command mode and interrupts user data transmission, but it does not end the data connection. Therefore, this allows the user to issue commands while the connection is maintained. extended AT-command. Extended commands were developed to provide greater functionality and control over modem operations than is available from the basic AT command set. fax mode. The modem is in fax mode when, through use of fax communications software, it can send and receive faxes, and set certain fax-related features. Note that the modulation protocol used by the modem in fax mode is also different from the usual data mode modulation. flow control. The method that enables the DTE and DCE to regulate the flow of data between themselves. Software flow control (XON/XOFF) uses the ASCII characters XON (Control-Q) and XOFF (Control-S) to start and stop the data flow. Hardware flow control (RTS/CTS) uses the RS-232 signals RTS and CTS to start and stop the data flow. full-duplex. Two-way simultaneous transmission between modems, which can occur via a four-wire circuit on a leased line, or with a two-wire connection when the frequency bandwidth is divided into two distinct channels, or when echo cancellation is employed (for instance, Bell 103, 212, and V.22 use frequency division, while V.32 uses the echo cancellation). guard tone. Guard tones are used in the United Kingdom and other countries. This requires that the modem transmit an 1800-Hz tone after it sends an answer tone. The guard tone is controlled by the &G command. Guard tones are not used in the U.S.A. half-duplex. Signal flow in both directions, but only one way at a time with each modem alternating between send and receive. Hayes Compatible. Hayes Microcomputer Products, Inc. developed the AT command set, which has become a de facto industry standard. Hayes commands are always initiated with an AT(attention code) prefix. hook flash. The dial modifier(!) causes the modem to go on-hook (hang-up) for one-half second. ITU-T. The Telecommunications Standardization Sector of the International Telecommunications Union. See CCITT. LAPM. Link Access Protocol for Modems. A V.42 ARQ type of error correction protocol that is controlled by S-register 46. LAPM can be activated with or without V.42bis data compression. leased line. Also referred to as a private line. A leased line is obtained from a communications company (carrier) to provide a transmission medium between two points. The line consists of a permanent dedicated circuit between two points, or to a set of previously arranged points. This is in contrast to switched or dial-up lines, which can be connected to any point on the network. line modulation. The means by which a carrier is varied to represent a signal carrying information. In a modem, the user's digital data is used to modulate the modem's transmitter carrier to allow the digital signal to be carried over analog facilities. long space disconnect. Determines whether the modem disconnects when it receives a continuous break from a remote modem. Controlled by the ATY command. loopback tests. There are four types of loopback tests: 1. The local digital loopback tests the operation of the DTE, including whether data is leaving the terminal or computer port. 2. The local analog loopback tests the digital and analog circuits of the modem. 3. The remote digital loopback checks the operating condition of the line and remote modem. 4. The remote analog loopback tests the line to the remote modem. MNP. Microcom Networking Protocol. A series of data communications protocols developed by Microcom for full-duplex, error-free communications. modulation handshake. Also referred to as Automode Enable and is controlled by the ATN command. This determines whether the modem must connect at a particular speed, or allow connection at any speed supported by both modems. negotiation fallback. Controlled by S-register 36 as part of the V.42 protocol. Setting this register indicates what action to take when a desired connection cannot be made (either hang-up, direct mode connect, or normal mode connect). non-volatile RAM. Also NVRAM. Random access memory whose data is retained when power is turned OFF. This is especially useful for modems to store user- defined default configuration settings. These settings would be loaded into modem RAM at power-up. online state. Same as data mode. To transmit or receive data, the modem must be in the online state. When placing a call, the modem is put online when Data Carrier Detect (DCD) goes high. PBX. Private Branch Exchange. A telephone switching system at a customer site. pulse dialing. Also referred to as rotary dialing (like dialing with the older-style rotary dial wheel). The dial modifier ATP sets the modem to pulse dialing, which is the default method, as opposed to tone dialing (push button touch-tone), which is enabled with ATT. All telephone exchanges will accept older-style pulse dialing and most exchanges will accept modern tone- dialing. result code. A response sent by the modem after processing a command. The response reports the modem's status or the progress of a call and can take the form of either digits (numeric) or words (verbose). Issuing a V1 command enables word responses. A V0 (V-zero) command enables numeric responses. The Q1 command disables their use entirely. Example: OK (word), or 0 (numeric) indicates that the modem successfully processed a command. retrain. An adjustment process performed when one of the modems detects signal distortion or line noise that threatens data integrity. RTS/CTS. Request to Send/Clear to Send. RTS and CTS are two control signal lines between the modem (DCE) and the terminal (DTE) that allow the terminal to control the flow of information. Also see flow control. sleep inactivity timer. Determines the length of time the modem operates in normal mode with no activity before returning to low-power sleep mode. standard AT-command. The basic AT command set, originated by Hayes Microcomputer Products, Inc. synchronous clock source. Applies to synchronous modem operations and is set with the &X command. The command specifies the clocking source referred to as the transmit signal element timing. This can be controlled by either the modem or the terminal. synchronous communications. A method of transmission in which data bits are sent continuously at the same rate under the control of a fixed frequency clock signal. touch-tone dialing. Push-button tone dialing as used on contemporary phone sets. The dial modifier ATT sets the modem to tone mode. XOFF. Transmitter Off. A control character that instructs the DTE to suspend transmission. See also flow control. XON. Transmitter On. A control character that instructs the DTE to start or resume transmission. INDEX $H 3-16 +++ 3-1 16550 UART 5-5 ASB 4-7 (automatic speed buffering) 5-2, 5-4, 5-5 asynchronous mode 3-13 asynchronous transmissions 4-5 asynchronous/synchronous mode selection 3-12 auto-reliable buffer 3-18 automatic speed buffering 4-7 backspace character 2-2 Bell 103 4-4 Bell 212A 4-4 blind dialing wait time before 2-2 BREAK control 3-19 BREAK handling options 2-5 buffer lower limit 2-5 buffer upper limit 2-5 call waiting disable 3-3 caller ID. function 3-21 calling card prompt tone see dial modifier 3-3 carriage return character 2-1 carrier detect response time 2-2 carrier selector 2-9 change contents of referenced S-Register 3-7 command $H 3-16 %C 3-17 %CCID 3-21 %DUMBn 3-17 %En 3-17 %L 3-18 %Q 3-18 &An 3-11 &Bn 3-11 &Cn 3-11 &D 2-3, 2-4, 3-2, 3-10 &Dn 3-11 &F 4-2, 5-5 &F1 4-2, 4-3 &F2 4-8 &F3 4-3, 4-8 &Fn 3-12, 4-2, 4-3, 5-4, 5-5 &Jn 3-12 &K 5-1, 5-4 &K6 5-4 &K7 5-4 &Kn 3-12, 3-20 &Ln 3-12 &Mn 3-12 &Q 2-3, 2-4, 5-2, 5-3, 5-4, 5-5 &Rn 3-13 &Sn 3-13 &T 2-3 &Tn 3-13 &Un 3-14 &V 3-15, 4-2 &W 2-2, 4-1, 4-2 &Wn 3-15 &Yn 3-15 &Z 3-4 &Zi=n 3-16 +++ 3-1, 4-5 =x 3-7 ? 3-7, 4-3, 4-4 A 3-1 A/ 3-1 An 3-18 asynchronous/synchronous mode selection 3-12 AT 3-1 AT&Q4 4-7 AT&Q6 4-7 AT&Qn 2-3 AT&Rn 2-3 auto-reliable buffer 3-18 Bn 2-4, 3-2, 3-18 BREAK control 3-19 caller ID. function 3-21 change contents of referenced S-Register 3-7 Cn 3-18 command line prefix 3-1 connect as answering/originating modem 3-11 data compression 3-17 data echo 3-18 data set ready options 3-13 data terminal ready options 3-11 DCD 3-11 dial modifier 3-2 dial telephone number 3-2 disable automatic retrain 3-11 display contents of referenced S-Register 3-7 Dn 3-2 DSR 3-13 DTE auto rate adjustment 3-19 dumb mode 3-17 echo command characters 3-4 En 3-4, 3-18 enable/disable result codes 3-7 escape sequence 3-1 flow control modem-to-modem 3-18 flow control options 3-20 Gn 3-18 go on-line in answer mode 3-1 Hn 3-4 identification request 3-4 In 3-4 inactivity timer 3-20 Jn 3-19 Kn 3-19 leased line operation 3-12 line quality monitor 3-17 line signal level 3-18 line signal quality 3-18 Ln 3-6, 3-19 load factory profile 3-12 local and end-to-end flow-control options 3-12, 3-20 maximum MNP block size 3-18 Mn 3-6 MNP block/stream mode 3-19 modem reset 3-11 modulation fallback options 3-6 negotiation progress message options 3-10 Nn 2-4, 2-9, 3-6, 3-20 On 3-6 on-line escape sequnce 3-1 on-line status 3-20 operating mode 3-20 P 3-7 point to new S-Register 3-7 Qn 3-7, 3-20 reading S-Registers 3-7 repeat last command 3-1 retrun to on-line mode 3-6 RTS/CTS options 3-13 S 3-20 select data carrier detect option 3-11 select extended result code function 3-10 select long space disconnect function 3-10 select protocol compatibility 3-2 select result code format 3-8 select stored profile on power-up 3-15 set pulse dial mode 3-7 set tone dial mode 3-8 Sn 3-7 Sn= 4-3 Sn=x 3-7 Sn? 3-7, 4-3 speaker control 3-6 speaker volume 3-6 store telephone numbers 3-16 store user profile 3-15 switch hook control 3-4 T 3-8 telephone jack selection 3-12 test mode options 3-13 Tn 3-20 transmit break to remote 3-18 trellis code modulation, enable/disable 3-14 Un 2-10 view help information 3-16 view stored paramters 3-15 Vn 3-8, 3-21 W 4-8 Wn 3-10 writing to S-Registers 3-7 Xn 3-10, 3-21 XON/XOFF flow control 3-21 Yn 3-10 Z 4-3 Zn 3-11 command line prefix 3-1 command mode 4-5 command processor 4-5 command;DTR 3-11 compression ratio, data 5-2 conditional compression &Q9 5-2, 5-3, 5-5 configuration set ASB mode 5-5 set direct mode 5-4 set factory defaults 5-4 set MNP/4 mode 5-5 set V.42bis or MNP/4 mode 5-5 connect as answering/orininating modem 3-11 connection failure cause codes 2-6 control-Q see, flow control - software 5-4 control-S see, flow control, software 5-4 CRC see, cyclic redundancy check 4-4 current DCE speed 2-4 cyclic redundancy check 4-4 D data flow control 5-3 local flow control 5-3 data carrier detect see, DCD 4-5 data compression 3-17 compression ratio 5-2 conditional &Q9 5-2, 5-3, 5-5 protocols 4-4 data compression selection 2-5 data echo 3-18 data set ready options 3-13 data terminal ready see, DTR 4-5 data terminal ready options 3-11 DC1/DC3 see, flow control, software 5-4 DCD 2-2, 3-11 (data carrier detect) 4-5 defaults Apple Macintosh hardware handshaking 4-3 Hayes-compatible 4-2 IBM-compatible 4-2 delay before forced hang-up 2-4 dial digits 3-2 dial last number see dial modifier 3-4 dial modifier 3-2 delay dial sequence (,) 3-2 dial last number (L) 3-4 dial stored number (S) 3-4 flash, initiate (!) 3-3 initiate flash (!) 3-3 originate call in answer mode (R) 3-4 pause see delay dial sequence (,) 3-2 pulse dial (P) 3-4 return to command mode after dialing (;) 3-3 substitute digits for letters (") 3-2 tone dial (T) 3-4 wait for bong ($) 3-3 wait for dial tone (W) 3-3, 3-4 wait for silence before dialing (@) 3-3 dial stored number see dial modifier 3-4 dial telephone number 3-2 disable automatic retrain 3-11 display contents of referenced S-Register 3-7 distinctive ring settings 2-7 dropped characters 5-5 DSR 3-13 DTE auto rate adjustment 3-19 DTMF dialing speed 2-2 DTR 3-11 (data terminal ready) 4-5 DTR detection 2-3 Dumb Mode E-1 dumb mode 3-17 E EC (see, error control) 5-1 echo command characters 3-4 enable/disable result codes 3-7 end-to-end flow control 5-4 error control 5-1 protocols 4-4, 5-2 escape code 2-1 escape code guard time 2-2 escape sequence 3-1 F file transfer failures 5-1 file-transfer protocols 4-4 Kermit 5-4 XMODEM 4-4, 5-1, 5-4 YMODEM 4-4, 5-4 ZMODEM 5-3 flow control 5-1 data 5-3 end-to-end 5-4 hardware (RTS/CTS) 5-1, 5-4 local 5-1, 5-3, 5-4 modem-to-modem 3-18 software (XON/XOFF) 5-4 Control Q 5-4 Control S 5-4 DC1 5-4 DC3 5-4 flow control options 3-20 frequency shift keying 4-4 FSK see, frequency shift keying 4-4 G go on-line in answer mode 3-1 H Hayes autosync 4-7 high speed serial port 5-6 I IBM-compatible defaults 4-2 identification request 3-4 inactivity timer 2-3, 3-20 indicator lights CD 3-7, 3-11 initiate flash see dial modifier 3-3 ITU-T V.22 4-4 V.22bis 2-7, 4-4 V.32 3-14, 4-4 V.32bis 2-9 V.42 5-1, 5-2, 5-3, 5-5 V.42bis 4-4, 5-2, 5-5 K Kermit 5-4 L LAP-M (link access protocol for modems) 4-5, 5-2, 5-3, 5-5 LAP-M packet size 2-10 last ring type detected 2-9 leased line operation 3-12 line quality monitor 3-17 line signal level 3-18 line signal quality 3-18 linefeed character 2-1 link access protocol for modems see, LAP-M 5-2 link statistics display 3-5 load factory profile 3-12 local and end-to-end flow-control options 3-12, 3-20 local flow control 5-3 lost carrier to hang-up delay 2-2 M Macintosh factory defaults 4-3 hardware handshake 4-7 cable 4-7 hardware handshaking defaults 4-3 maximum DCE speed 2-4 maximum MNP block size 3-18 MNP (Microcom Networking Protocol) 4-5, 5-1, 5-2, 5-5 Class 2 5-2 Class 3 5-2 Class 4 5-2, 5-5 Class 5 4-4, 5-2, 5-3 error-control 5-2 MNP 10 2-8 MNP block/stream mode 3-19 MNP class 10 options 2-8 MNP result codes 3-21 mode ASB 4-7 asynchronous 4-5 command 4-5 DMA enhanced 5-6 Hayes autosync 4-7 on-line 4-5 synchronous 4-6 modem factory defaults 4-2 modem reset 3-11 modem test timer 2-3 modem-to-modem flow control 3-18 modulation fallback options 3-6 N negotiation message options 2-6 negotiation progress message options 3-10 O on-line escape sequence 3-1 on-line mode 4-5 on-line status 3-20 operating mode 3-20 originate call in answer mode see dial modifier 3-4 P parameters power-up 4-1 pause see dial modifier 3-2 pause time for command dial modifier 2-2 PC-HSSP 5-6 point to new S-Register 3-7 possible speeds selector 2-9 private circuit carrier level 2-5 ProClass high speed serial port 5-6 protocol negotiation fallback 2-3 protocols Bell 103 4-4 Bell 212A 4-4 data-compression 4-4 error-control 4-4, 5-2 file-transfer 4-4 pulse dial see dial modifier 3-4 Q QAM (quadrature amplitude modulation) 4-4 R reading S-Registers 3-7 repeat last command 3-1 retrain 3-7, 3-11 return to command mode after dialing see dial modifier 3-3 return to on-line mode 3-6 ring count 2-1 ring to answer on 2-1 RS232 clear to send 4-6 data 4-6 data set ready 4-6 data terminal ready 4-7 HS--secondary RLSD 4-6 pin 1 4-6 pin 12 4-6 pin 15 4-7 pin 17 4-7 pin 2 4-6 pin 20 4-7 pin 22 4-7 pin 24 4-7 pin 3 4-6 pin 5 4-6 pin 6 4-6 pin 7 4-6 pin 8 4-6 protective ground 4-6 receive clock 4-7 receive data 4-6 ring indicator 4-7 serial interface 5-4 signal ground 4-6 transmit data 4-6 transmitter clock 4-7 RS232/pin 4-6 RTS/CTS (Request to Send/Clear to Send) see, flow control 5-1 delay time 2-3 RTS/CTS options 3-13 S S-Register backspace character 2-2 BREAK handling options 2-5 buffer lower limit 2-5 buffer upper limit 2-5 carriage return character 2-1 carrier detect response time 2-2 carrier selector 2-9 connection failure cause codes 2-6 current DCE speed 2-4 data compression selection 2-5 delay before forced hang-up 2-4 distinctive ring settings 2-7 DTMF dialing speed 2-2 DTR detection 2-3 escape code character 2-1 escape code guard time 2-2 inactivity timer 2-3 LAP-M packet size 2-10 last ring type detected 2-9 linefeed character 2-1 lost carrier to hang-up delay 2-2 maximum DCE speed 2-4 MNP class 10 options 2-8 modem test timer 2-3 negotiation message options 2-6 pause time for comma dial modifier 2-2 possible speeds selector 2-9 private circuit carrier level 2-5 protocol negotiation fallback 2-3 ring count 2-1 ring to answer on 2-1 RTS to CTS delay interval 2-3 S0 2-1, 3-1, 4-3, 4-4 S1 2-1, 4-1 S2 2-1, 3-1 S3 2-1, 4-1 S4 2-1, 4-1 S5 2-2, 4-1 S6 2-2 S7 2-2, 3-3, 4-4 S8 2-2 S9 2-2 S10 2-2 S11 2-2 S12 2-2, 3-1 S18 2-3 S24 2-3 S25 2-3, 3-11 S26 2-3, 3-13 S30 2-3 S36 2-3, 5-2 S37 2-4, 2-9 S38 2-4 S43 2-4 S46 2-5, 5-2, 5-5 S48 2-5 S49 2-5 S50 2-5 S63 2-5 S82 2-5 S86 2-6 S95 2-6, 3-10, 4-8, 5-5 S97 2-7 S101 2-7, 2-8 S102 2-9 S108 2-9 S109 2-9 S110 2-9 S136 2-10 signal quality selector 2-9 sleep inactivity timer 2-3 V.32 automode V.22/V.22bis probe timing 2-7 V.42 feature negotiation action 2-5 wait for carrier after dial 2-2 wait time before blind dialing 2-2 select data carrier detect option 3-11 select extended result code function 3-10 select long space disconnect function 3-10 select protocol compatibility 3-2 select result code format 3-8 select stored profile on power-up 3-15 serial drivers 5-6 serial ports 5-6 set pulse dial mode 3-7 set tone dial mode 3-8 signal quality selector 2-9 sleep inactivity timer 2-3 speaker control 3-6 speaker volume 3-6 store telephone numbers 3-16 store user profile 3-15 substitute digits for letters see dial modifier 3-2 switch hook control 3-4 synchronous mode 3-13 synchronous transmissions 4-6 T telephone jack selection 3-12 telephone numbers, store 3-16 test mode options 3-13 tone dial see dial modifier 3-4 transmit break to remote 3-18 trellis code modulation, enable/disable 3-14 U UART 5-5 universal asynchronous receiver/transmitter 5-5 V V.32 automode V.22/V.22bis probe timing 2-7 V.42 feature negotiation action 2-5 view help information 3-16 view stored parameters 3-15 W wait for bong see dial modifier 3-3 wait for carrier after dial 2-2 wait for dial tone see dial modifier 3-4 wait for silence before dialing see dial modifier 3-3 wait time before blind dialing 2-2 writing to S-Registers 3-7 X XMODEM 4-4, 5-1, 5-4 XON/XOFF flow control 3-21 Y YMODEM 4-4, 5-4 Z ZMODEM 5-3