Serial Port Problem

  • Thread starter Thread starter raycope
  • Start date Start date
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raycope

Hello, I am using my PC comm port to talk to another system which uses
the same
(industry standard 8250/16450) UART. When I remove the serial cable
and re-install it,
the system stops receiving chars from the PC. Another words, no many
how many times
I hit the ENTER key on my PC terminal, the system doesn't respond
(using Procomm I
see the SD lite flash when I hit ENTER, but the system doesn't
respond). However, when
the system outputs a message, this still shows up on the PC side.
Removing and re-
installing the cable seems to stop transmit but doesn't effect receive
from the PC point-of-
view.

The only way I've found to workaround this problem is to reset the
system (not the PC, the
external system). This always fixes it, but I would like to know if
there is any other way to
get the serial port to work again without having to reset the system?
Thanks for any help
you can provide.
 
raycope said:
I am using my PC comm port to talk to another system which uses
the same (industry standard 8250/16450) UART. When I remove
the serial cable and re-install it, the system stops receiving chars
from the PC. Another words, no many how many times I hit the
ENTER key on my PC terminal, the system doesn't respond
(using Procomm I see the SD lite flash when I hit ENTER, but
the system doesn't respond). However, when the system outputs
a message, this still shows up on the PC side. Removing and re-
installing the cable seems to stop transmit but doesn't effect
receive from the PC point-of-view.

The only way I've found to workaround this problem is to reset the
system (not the PC, the external system). This always fixes
it, but I would like to know if there is any other way to get the
serial port to work again without having to reset the system?
Click to expand...

Do you have flow control enabled and configured properly at both ends?
Are the ports set for proper handling of the handshaking signals, with
none left unconnected or grounded? If all those are correct, try a
diagnostic with a loopback plug.

If you're using the Windows version of Procomm, you may need to change
to a 16550A or other buffered UART instead of the 8250/16450.

I suggest you not plug or unplug the serial cable with the power on
since modern serial ports lack the rugged buffers found in older ones.
Damage is not always complete and may destroy charge pumps or output
transistors and still allow operation at lower speeds.
 
I ahve very limited experience with Procomm and it was a long time ago.

However I have programmed serial ports with VB6 using the MSComm object. I
too have had similar stability problems, my solution was to open the port,
transmitt or recieve, and then close the port, and do this each time data
needed to be transferred. This solved my problem because the instability
stemmed from trying to open and already open port (due to some sort of
interruption like the cable being diconnected) or having the out buffers not
flushed because of some sort of interuption.

I do not know if there is a solution for you in the above paragraph if you
are using Procomm, however now you know you are not alone in this problem.
(for whatever that's worth)
 
The system is setup for **software flow control** which is somewhat
unusual but a requirement for our application. Is there something I
can do from the terminal side (using Procomm or HyperTerm) that will
make it work again without reseting system? That's
the kind of solution I'm looking for. Thanks for any
advice you have.

P.s.- For what it's worth, the RS233 drivers are pretty robust and I
have never had a problem damaging a part by removing or installing
cable.
 
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