> -----Original Message-----
> > Pin 5 is an odd extra ground on the M100. Pin 7 is the ground for the
> > spec, all wands, and all machines with the port, including the 100.
>
> fair, but pin5 is ground on an RS-232 DB-9. So, that is what I used on
> MVT100. I think in the future I will just wire both to ground on the
> MVT100 board.
> [...]
> on second thought you are right, ground should be on pin 7 since it is a
> TTL port. It isn't an RS-232.
Hmm... Well, if I may add my two cents' worth here...
When performing the BCR hack, transmitted data is wired to be sent out the
unused pin 3 in order to make interfacing with MVT100 easy using a standard
serial cable (it's already wired to receive on pin 3 from RS-232 devices). The
fact that the M100 already has pin 5 grounded is an easy convenience, but for
the T102 (and maybe the T200 in the future) adding a ground jumper to pin 5 in
the computer seems to me to be the right way to go. If you ground pin 7 in the
MVT100, it's going to drag down the computer's RTS signal whenever it's plugged
in to an actual RS-232 interface. Granted, RS-232 is supposed to be able to
tolerate that, but it seems unnecessary.
Since the MVT100 is meant to connect to either RS-232 or the hacked BCR, I'd
rather see the design of the MVT100 stay RS-232-friendly and put the onus upon
the BCR hacker to supply TD on pin 3 and ensure there's a ground on pin 5
(since they have to go inside the machine to perform the BCR hack anyway).
jim
