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From: curtis@se-sd.SanDiego.NCR.COM (Curtis Johnson)
Newsgroups: comp.windows.ms.programmer
Subject: com port problem and MSW
Message-ID: <4460@se-sd.SanDiego.NCR.COM>
Date: 1 Mar 91 22:34:53 GMT
Reply-To: curtis@se-sd.SanDiego.NCR.COM (Curtis Johnson)
Organization: NCR Corp., Systems Engineering - San Diego
Lines: 42



I'm debugging a problem that occurs in an RS232 communications
manager that runs under MSW3.0.  This product provides a user
interface to a mini-computer via MS Windows.

The symptom that we're concerned with is that serial data
apparently gets lost somewhere between the serial port and
MS Windows.

By attaching a serial communications analysis system between
the serial port and the cable I can see that the data is going
into the PC.  Comparing that data with the data displayed on
a debug monitor (from some debug code inserted immediately
after the call to ReadComm()), I can see that the data coming
into the port is different than the data in the buffer
returned by ReadComm().  Usually this data is 200 - 300
characters of a login banner message.  Sometimes a line or two
is missing and sometimes just one or a few characters are
missing.

We're only seeing these problems on AT's, 386SX/MC and 486MC
machines.  These symptoms don't appear on 386DX machines.
Also, these symptoms don't occur on *every* AT, 386SX/MC and
486MC we've tried.  We've only tried PC's manufactured by one
company (guess who) and some will work properly and some won't.
We haven't found a common factor yet.

The serial port is opened by calling OpenComm() with a value
of 6144 for the input buffer size and a value of 2176 for the
output buffer size.  Other smaller values have been tried (1024
and 512 for both) with the same results.  The symptoms occur at
19200, 9600, 4800, 2400 and 1200 baud with a 7 bit data size,
one stop bit and even parity.  The symptoms occur when the PC
is connected directly to the serial port of the other computer
and when connected through a modem.

Any ideas?  Sure could use some help on this one.  Thanks.

--
curtis@se-sd.sandiego.ncr.com
(619) 693-5685