Article 158187 of comp.os.vms:
Doug Cain wrote:
> 
> In article <3274D017.70F915CF@star.enet.dec.com>,
>    Fred Kleinsorge <kleinsorge@star.enet.dec.com> wrote:
> 
> >  The tablet is a Summagraphics Bitpad-II with modified microcode.  To make
> >  it work on a PC, you would have to know the pin out of the connector, and
> >  hook it up to a serial line, and correct power supplies.  Then you would
> >  need the data format, and write a driver for it.
> >
> >  No small task.
> >
> I would hope that whoever modified the microcode in the Summagraphics to turn
> it into a "DEC" product has repented.  Perhaps if the code is in PROM you
> could "update" it into a real Summagraphics.  I have turned some Calcomp
> boards into Tektronics boards this way.
> 


  Maybe yes, and maybe no.

  I certainly was highly in favor of the modified firmware at the time, since I had
  just spent time figuring out how to support a dozen different mouse and tablet
  protocols on the PRO-300.  When I was asked to review it, I *liked* the changes...
  and you must remember that at the time (early 80's) the world was not dependent
  on having a Windows compatable driver ;-)

  Tablets and mice had (and have) half-assed protocols designed for them.  Most of them
  supported multiple formats, and very few of them supported any command that would identify
  the device.  Heck, the standard PS2 mouse that we all know and hate doesn't have a way
  of telling which byte is the first byte of three.  And the new (and very nice) Calcomp
  tablet powers up in *RUN* mode - talk about stupid - 99% of the time you want incremental
  stream mode - and nobody wants to waste the CPU cycles handling character interrupts when
  *nothing* has happened to the tablet position or buttons (or deal with a stream of data
  being thrown at the system during power up and booting).

  The VSXXX-AB was designed to replace the mouse, and to provide a way to allow the system
  to determine what it was, and to not require a seperate power supply (which my MM960
  needed for instance, as does my Calcomp).  The data format isn't much different than any
  of the common 5-byte binary formats used by half a dozen tablets.

  In any case, you can find the documentation of the HW and the protocol in the VCB02
  technical reference manual (of all things, this is the GPX graphics device specs).  I
  don't have the order number handy, and it's been so long it may be out-of-date.

  But if you are not in a hurry, and I have the time - I will type up the relevant info
  and publish it here.


   _Fred