Q318784: PRB: MSComm.Input returns comReadError (8020) with Some Ports

Article: Q318784
Product(s): Microsoft Visual Basic for Windows
Version(s): 6.0
Operating System(s): 
Keyword(s): kb3rdparty kbCommPort
Last Modified: 10-MAY-2002

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The information in this article applies to:

- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
- Microsoft Visual Basic Learning Edition for Windows, version 6.0 
- Microsoft Visual Basic Professional Edition for Windows, version 6.0 
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SYMPTOMS
========

When you use the Input method of the MSComm control with some serial ports, the
MSComm.Input method may fail, and you may receive the comReadError error (error
8020).

CAUSE
=====

This problem occurs because MSComm.Input reads only the bytes that are
immediately available in the serial driver. By design, MSComm.Input does not
return any bytes if the serial driver has not received any bytes. Because the
MSComm control does not expect the ReadFile method to return ERROR_IO_PENDING,
MSComm returns the comReadError error if this occurs.

RESOLUTION
==========

A serial driver should return SUCCESS synchronously for all read requests that
can be immediately fulfilled with data that is currently present.

This problem is only known to occur with some third-party serial drivers. To
correct the problem, contact the manufacturer of the serial driver to obtain an
updated driver.

Additional query words: MSCOMM32.OCX error reading comm device

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Keywords          : kb3rdparty kbCommPort 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVB600
Version           : :6.0
Issue type        : kbprb

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