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Q163333: Autosynch Compatible COM Applications May Fail w/ FIFO Enabled

Article: Q163333
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbenv kbnetwork
Last Modified: 09-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation version 4.0 
- Microsoft Windows NT Server version 4.0 
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SYMPTOMS
========

The released version of the Windows NT 4.0 serial port driver (Serial.sys) does
not delimit data in a manner compatible with the Hayes AutoSynch standard when
FIFO is enabled on the COM port. For example, IBM PCOMM implements the Hayes
AutoSynch standard and requires that data to be delimited be compliant with the
AutoSynch standard to operate reliably.

CAUSE
=====

The Hayes AutoSynch standard requires that data be delimited with an escape
character followed by a line status error with data. The last part of an
AutoSynch frame is indicated by line status error data with the parity error bit
enabled followed by 02. In this case, FIFO was enabled, buffering data on the
COM port, and Serial.sys would return only part of the data delimited
correctly.

For example the following data

  FF BF FB BD

should return from Serial.sys as

  7D 01 E1 FF 7D 01 E1 BF 7D 01 E1 FB 7D 01 E1 BD 7D 01 E5 02

where 7D is an escape character, 01 indicates a line status error, and E1 is the
line status error data (E5 is line status error data with the parity error bit
enabled). The released version of the Windows NT 4.0 Serial.sys driver returns
the following unusable stream:

  FF 7D 01 E1 BF FB 7D 01 E1 BD 02

RESOLUTION
==========

The file Serial.sys was modified to correctly insert an escape character
followed by a line status error with data when returning buffered data from
FIFO.

The updated file has been posted to the following Internet location:

  ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP2/serial-fix

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This
problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack.
For information on obtaining the service pack, query on the following word in
the Microsoft Knowledge Base (without the spaces):

  S E R V P A C K


Additional query words: prodnt

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Keywords          : kbenv kbnetwork 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : winnt:4.0

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