> Now I have a doubt regarding null modem cable.
> Using 2 9 pin to 25 pin connectors,I made a null modem cable. 9 pin ends
> of the cable were connected to the machines(COM ports).
> Before going to remote debugging, I wanted to check whether back-to-back
> connection is proper or not. So I wrote into the COM port of the
> development m/c (/dev/ttyS0) and tried it read on
> the target m/c from the COM port (/dev/ttyS0) using "cat" command
> as follows:
>
> Dev. m/c:
> cat <file> > /dev/ttyS0
>
> Tar m/c
> cat /dev/ttyS0
>
> Unfortunately the expected is not happening.
> First of all, I want to know the null modem cable which I'm using is
> proper.
Sounds like rx and tx are not right (not null modem).
Do you have / have access to a multi-meter. The easiest way is to check
if its a good null modem (no flow control) is to make sure that rx and
tx are correct. Basically you can check to see if the pins swap on each
end. Rx and Tx should the top middle and top right or top middle and
top left depending on if its a male or female end. This can be difficult
to do if its the female end, but can be done (with some wire).
Another thing that you might to check is how the flow control is done. I
have actually seen a lot of NULL modem cables that do the flow control
pins on NULL modems incorrectly. This is fine as long as Hardware Flow
Control is never used.
You may / may not want to try using minicom on either side to just test
it by typing data back and forth. You can also do that between 2 serial
ports on your pc (ttyS0<->ttyS1) if that is easier for you to test.
Brad (bremedios@intrinsyc.com)
