Re: RS-232 DB25 MUX connection question

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Lewis Gardner" <lgardner@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:43d688c3$1_1@xxxxxxxxxxxxxxxxx
> Robert Green wrote:
> > I've got a MUX with a DB-25 connector on the back.  The manual tells me
that
> > the pins are arranged as follows:
> >
> > 01  -  Alarm Input 1
> > 02  -  Alarm Input 2
> > 03  -  Alarm Input 3
> > 04  -  Alarm Input 4
> > 05  -  Alarm Input 5
> > 06  -  Alarm Input 6
> > 07  -  Alarm Input 7
> > 08  -  Alarm Input 8
> > 09  -  RS-232 RX Input
> > 10  -  RS-232 TX Input
> > 11  -  RS-232 RX Output
> > 12  -  RS-232 TX Output
> > 13  - VCR Trigger Input
> > 14  -  Alarm Input 9
> > 15  -  Alarm Input 10
> > 16  -  Alarm Input 11
> > 17  -  Alarm Input 12
> > 18  -  Alarm Input 13
> > 19  -  Alarm Input 14
> > 20  -  Alarm Input 15
> > 21  -  Alarm Input 16
> > 22  -  Alarm Hold Input
> > 23  -  Alarm Output Common
> > 24  -  Alarm Output NC
> > 25  -  Alarm Output NO
>
> > Does anyone have any suggestions how to wire the MUX pinout above so
that I
> > can communicate with it via a 9 or 25 pin PC serial port?
>
> RS-232 only requires 3 wires TX RX and ground for non-hardware
> handshaking communication. On a 9 pin connector those are on pins 3, 2
> and 5 respectively. No standard serial cable is going to work with the
> pinout you have listed above.

I didn't think so.  But the bigger problem is:  Which pin on the MUX is a
ground pin?

> 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>


> In an earlier post you mentioned "these MUX boxes have a RS-485 port to
> connect to each other". Is it possible that pins 9 thru 12 are actually
> RS-485 which uses 4 wires?

Very doubtful since it also has two jacks using what look like CAT-5
connectors labelled "RS-485 IN" and "OUT" below the DB-25 connector.
Creating a null modem cable to connect the two units seems pretty
straightforward - I think.  But first, I need to access the box via RS-232
because there's no point in interconnecting them if I can't talk to them.

> Do you have the serial protocol (baud, stop bit, parity and command
> structure) for this box?

I have a list of all the ASCII and hex commands it understands.  The
protocol is listed for the usual range of 1200-19600 settings.  There
doesn't seem to be much more about serial networking other than a pinout of
the RS-485 connection and which pins on that connector to short to terminate
the network.

Thanks for the response!

--
Bobby G.