There is a free tool called TALBreakout avbailable at the following
URL that should do what you require quite nicely.
http://www.taltech.com/freesoftware/fs_sw.htm

Download the TALBreakout program and read the help file to see how it
works. Basically it is designe to run in a PC with two serial ports
where you connect the PC in between another PC and a device - i.e.
like a breakout box. It then displays everything that goes through the
serial line in both directions.



On 30 Oct 2003 09:36:56 -0800, (Chris Campbell)
wrote:

I need to be able to look at the bits/bytes going back and forth on a
serial line. I don't really need to *emulate* anything in particular,
like *be* the DTE or DCE, I just want to sniff the line that two other
devices are talking on so I can troubleshoot. Besides RS232, I need
it to do 422 and maybe 485 (e.g. address filtering). This is for
pretty low speeds -- 38400 max and I could even live with just 19200.

The PC-based tool I'm using now just suuuuuucks. At a previous job we
had a small standalone HP analyzer which was extremely useful;
naturally I don't remember the model name but googling around leads me
to think it was an HP 4951x. That model apparently has some storage
capabilities -- I don't need that either (just a RAM capture is fine).

Can anyone suggest similar analyzers for this purpose? No SONET, no
STP/UTP, just plain old low speed serial lines ... Once I have some
models identified then I'll start looking for used units.

Thanks!