
 DRIVER MACRO-
    MUST CLEAR S.WRCV BIT BEFORE DO QIO ELSE WINDOW WHEN AST CAN
    COME IN AFTER QIO AND TAKE BC AS ADDRESS
(    MUST SET MB.ST1 TO ER.PND FOR RSX AS WELL AS RT, FOR CASE WHERE
2    NO WAIT I/O AND NOT ACTUALLY ISSUED QIO YET
<    MUST CHECK FOR S.WAIT BIT SET BEFORE WAITING ON EF. 
F  
P CDERRM -
Z    CHANGED LENGTH OF TXTLEN AND MAXLEN FOR CONSISTENCY
d   
n CDPACK -
x    MESSAGE BLOCK NOT RELEASED ON SUCCESSFUL CLOSE REQUEST