🚀 go-pugleaf

geb1@ra.msstate.edu (Granville Barker) writes:

>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.

> Any ideas??


>Thanks,

>Granville Barker
>geb1@isis.msstate.edu


  I'm not surprised it dosn't work.  First of all RS232 signals are not 0v and 
some +ve voltage.  A 1 is -5 to15v and 0 is +5 to 15v ( I think I've got this
the right way round).  0v (-5 to +5) is indetermiate so strictly using diodes
to mix the signals shouldn't work.  It does work with some machines though as in real life an indterminate state has to be something.
 
 Second if both machines talk at the same time then the mixed signal will be
garbage, this setup will only work in half-duplex mode.  ( or simplex)

 You would have to use 2 serial ports to monitor 2 way conversations (and to
be able to tell where the data was comeing from).

 Chances are you only want to use this set up to occasionally check systems.
It would probably be easier to monitor each device seperatly - sending the same data.

			Hope this is of some help
				Garry

-- 
Mail:	Garry Wardrope, Computing Science Dept.,  Tel: (041) 339 8855 x5322
	Glasgow Univ., 17 Lilybank Gardens, Glasgow G12 8QQ, UK. 
email:	gjw@dcs.glasgow.ac.uk
".. and even if I came in sight of paradise what price its moon without Marsco"