Microsoft KB Archive/38530

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Sharing the COM Port in Windows with an Old Application

PSS ID Number: Q38530 Article last modified on 11-05-1993

1.x 2.x 3.00 MS-DOS

he information in this article applies to:
- Microsoft Windows Software Development Kit for Windows version 3.0


An old application that uses the serial port cannot share that serial port reliably with a Windows application. Characters may be lost during task switching. An old application that modifies the COMn port (where n is the COM port number) and is running under a .PIF file that does not activate the “directly modifies the COMn port” switch will cause this problem. Windows will allow any Windows application to use the COMn port. When the old application gives control of the port back to the Windows device driver, any information received by the COMn port may be lost during the switch. To solve this problem without allowing the old application to share the COMn port under Windows, activate the “directly modifies the COMn port” switch in the PIF Editor configuration session.

Additional reference words: 3.00 KBCategory: KBSubcategory: KrWoaMisc Copyright Microsoft Corporation 1993.