DOCUMENT:Q163333 [winnt] TITLE :Autosynch Compatible COM Applications May Fail w/ FIFO Enabled PRODUCT :Microsoft Windows NT PROD/VER:4.00 OPER/SYS:WINDOWS KEYWORDS:kbenv kbbug4.00 kbfix4.00 ------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Workstation version 4.0 - Microsoft Windows NT Server version 4.0 ------------------------------------------------------------------------- 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. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information. KBCategory: kbenv kbbug4.00 kbfix4.00 KBSubcategory: NTSrvWkst nthw Additional reference words: 4.00 prodnt ============================================================================ THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 1996.