Re: RS-232 DB25 MUX connection question

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Lewis Gardner" <lgardner@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:43d6cfa5$1_1@xxxxxxxxxxxxxxxxx
>
> >>>09  -  RS-232 RX Input
> >>>10  -  RS-232 TX Input
> >>>11  -  RS-232 RX Output
> >>>12  -  RS-232 TX Output
>
> >>My guess is that on pins 9 thru 12 two of those pins are grounds and the
> >>other two are TX and RX. The first check would be to probe those pins
> >>with a multimeter and see if any of 9 thru 12 were connected together.
> >>If they are those are likely the ground pin.
> >
> > Would you test for continuity with the unit off?  I'm only marginally
> > competent with electronics, I'm afraid.  I considered looking for
voltage on
> > the pins with the unit running, but wasn't sure which pin to use as
ground.
> > I was leaning towards pin 23  -  Alarm Output Common but it's really
just a
> > guess.  I suppose I could pop the case and try tracing the pins in
question
> > by eye.  <sigh>
>
> For the first bit of testing I would have the unit off and check for
> continuity between any two pins in the group 9 thru 12. If you find
> continuity between any of those two pins they are most likely ground.

That's what I will do to start.

> If there is no continuity between any of the pins you will need to open
> the thing up and start tracing. The ground pin(s) will likely go back to
> the biggest trace on the circuit board. I would stick to pins 9 thru 12
> for serial communications until I was sure something else was required.

I will visually trace the wire anyway just to be on the safe side.

> Once you have found the ground then sorting out the RX and TX is trial
> and error since "TX Input" and "RX Output" are fairly meaningless. Many
> serial devices will transmit a string when they power up. That is how I
> have found many a TD pin and the baud, data bit, parity and stop bit
> settings.

OK - that sounds like a plan.  It will be a while until the breakout box
arrives anyway.  Tonight I have to fire up the new PC to make sure all the
components are OK.  I'm glad to see AMD finally got smart and increased the
surface area of the CPU and beefed up the mounting of enormous 5 pound
cooling fan - increased to 80mm from the puny little 40mm fans of
yesteryear.  There's still a great satisfaction in cobbling all the separate
pieces together and getting it to light up and not burn up when you throw
the switch.

Thanks for your input, Lewis.  I appreciate it!

--
Bobby G.