Re: com port problem: it works on an Apple2, but not on a PC, why?

[wlsmith@valve.heart.rri.uwo.ca (Wayne Smith)]

In article <20b65u$jut@access.digex.net> kmccorm@access.digex.net (Kevin McCormick) writes:
>In article <1993Jun23.215637.11124@julian.uwo.ca> wlsmith@valve.heart.rri.uwo.ca (Wayne Smith) writes:
>>
>>We have an old Searle ISO-CAP Gamma counter that outputs data through
>>a serial line to an Apple ][.
>>
>>There are only 3 wires used: pins 1, 3 and 7.  Now, if this is standard
>>RS-232, then pins 1 and 7 are ground and 3 is the receive data line.
>>
>>Now, I wired in a female 25-pin connector in parallel and connected it to
>>a PC's serial port.  But with both the PC and the Apple running, the
>>Apple gets data but the PC doesn't register anything. (it also doesn't
>>work when connected to only the PC). 
>>
>>Are there any differences between Apple ][ and PC serial ports that 
>>can explain this situation?  ie does the Apple use a current-loop 
>>rs-232?  I temporarily moved the wire on pin 3 to pin 2 on the PC, 
>>but that didn't help.                 /^^^^^^^^^^^^^^^^^^^^^^^^^
---------------------------------------/

>Try wiring the one wire to pin 2 instead of 3.  Chances are one of the
>computers is wired as a DCE, the other as a DTE.  The Apple receives on pin 3,
>but the PC's trying to send on 3 and receive on 2.

I've read a bunch of RS-232 FAQ and info files, and 3 is supposed to be a
PC's receive line, but like I said pin 2 doesn't work either.  I've also read
that you're really not supposed to use pin 1 (chassis ground), at least
not at both ends, so maybe I'll cut it.

>If that still doesn't
>work, then it's possible that the PC is looking for hardware-handshaking
>signals that aren't present on the port.  Try disabling hardware-handshaking
>and ignoring other signals (like DCD, DTR, DSR, etc...)
>I hope this solves your problem!
>Kevin McCormick                           | "The more we try to control, the
>kmccorm@access.digex.net                  |  less we are really in control."

Gwbasic does report a time-out if I don't disable that stuff, so yes,
I do disable it.  3-wire comm port connections are common for PC's, 
but this is really a 2-wire situation, but that still shouldn't matter
as I'm not putting data out, just receiving.
-Wayne-