🚀 go-pugleaf

In article <geb1.715477196@Isis.MsState.Edu>,
geb1@ra.msstate.edu (Granville Barker) wrote:
 
> I am trying to build a RS-232 line monitor.  
> I want to connect it between two RS-232 devices, and have a wire comming 
> off that I can connect to another computer and monitor both sides of the
> conversation between the other two devices.  Ie.. a Plotter and a Computer.
> I need to see what is being transmited and received, I tried hooking 
> pins 2 and 3 to diodes, then connecting rx on the monitor computer to
> the other end of the diodes.  THe other 2 devices still communicate ok, but
> I never see anything on my monitor computer.  I am connecting ground.

I built something similar, but with an SPDT switch to select whether the
"monitor" was listening to the "terminal" or the "line".  Most of the
time you're only interested in one end of the conversation or the other.
Much of the time you are interested in both you can do the experiment
twice, once listening to one direction and again listening to the other.

When I need to see the relative timing I borrow the line monitor box from
our hardware people (multi thousand dollar box but using only 5% of its
capacity can monitor both sides of the line at once :-).

The only other general solution I can see is using a PC with two serial
ports, and doing the displaying of both sides in software.

BTW, the box I built had another SPDT switch that allowed substitution
of the "monitor"'s keyboard for that of the "terminal".  This came in
handy when the "terminal" (a macintosh) had crashed and I wanted to send
some command to the "line" (a mainframe).

zben@ni.umd.edu     -KA3ZDF