Serial Port problems

[Peter Jeremy]

In article <392 at stca77.stc.oz>, I wrote:
> I have been having problems with serial ports shutting down with the message
> "Garbage or loose cable on serial port xx, port shut down".  This has occurred
> on two different machines (ITT PS/440 and IBM PS/2), but only on ports talking
> to modems.  I am running Xenix/286 2.2.1 on both machines.

All of the replies have assumed that I was talking about login ports on smart
modems.  As I stated in my original article, the problem is occurring on
_leased-line_ (totally dumb) modems.  These modems are used to transfer data
between a continuously running application on the PC and another computer.
Getty is not involved.

Following some study of the _siointr routine in the kernel, as well as
applying rapid pulses to the various control lines, I have ascertained that
the system is highly resistant to noise when the non-modem invocation of the
serial port is used.  Since the incoming control lines (CTS, DSR, DCD) are
unnecessary for my application and the outgoing control lines are valid
whether modem or non-modem ports are specified, I have switched to using
the non-modem ports.  So far I have had no problems, but since it is an
intermittent fault, I will only ever know if I didn't solve the problem.
-- 
Peter Jeremy (VK2PJ)         peter at stca77.stc.oz
Alcatel-STC Australia        ...!uunet!stca77.stc.oz!peter
41 Mandible St               peter%stca77.stc.oz at uunet.UU.NET
ALEXANDRIA  NSW  2015