You can "bit-bang: other pins like dtr, rts etc. and with the use of 2
connectors make it look like the rx/tx lines. Alternately wire your
circuitry to these alternate pins. Be warned that you need to provide
external power to your curcuit since some ports a low power(2-4 ma).
Kevin E. Dodd
Embedded Systems Consulting
kevindod@triax.com
503.684-3731 Reached at
541.753-3633


-----Original Message-----
From:   Frank Mckenney [SMTP:rrs0059@IBM.NET]
Sent:   Thursday, March 12, 1998 5:49 AM
To:     PICLIST@MITVMA.MIT.EDU
Subject:        Re: Putting RS232 TX line high

>
> Does anyone know off-hand the memory address and value for setting the
RS232
> TX line high on a PC? I need to trigger a relay connected to this line.
>
> Thanks.
>
> C. Webb

Craig,

As other posters have pointed out, the serial ports on an Intel-PC
are built for sending and receiving "formatted" async bitstreams on
the TX and RX lines. As far as I know, there's no way of directly
bit-banging the TX and RX lines, which is what it sounds like you're
trying to do.

Why not use the modem control lines (RTS,DTR), as other posters have
suggested, and simply re-wire the cable to look at one of _those_
lines? Or, since some cables aren't easy to re-wire, pick up an
under-$10 "breakout" box from RadioShack(TechAmerica) and wire it
to cross (say) DTR on the Intel PC side to the cable's TX line?
Then just plugh teh adapter box into the circuit...

There may be reasons why this won't work ("It's an imperfect
universe" (;-); even so, if we can learn those reasons, it might
help define a better answer to your problem.

Hope this helps...


Frank McKenney            / OS/2 Advisor (OS2BBS)
McKenney Associates       / Richmond, Virginia / (804) 320-4887
Internet: rrs0059@ibm.net / TalkLink: WZ01123