Clear/Reset com port?

24 Oct 2006 3:21 PM

Rico

Hi Everyone,
Thanks for reading my post. I have a .net application written in C# that
uses RAS to create a dial up connection. My problem is once in a while, the
dial-up connection may drop, and I will receive an error,

Opening Port...
Error 633: the modem (or other connecting device) is already in use or is
not configured properly.

Can someone tell me how to clear or reset the com port?

Thanks

Rico

24 Oct 2006 4:13 PM

Dick Grier

Hi,

Usually (though not always, perhaps) this error is cause by a Virtual Serial
Port driver (used by USB and software modems). The driver fails to release
the port. If this is the case, I know of no way to clear it up. An updated
driver may be the only solution. I have not seen this when using a modem
that has a hardware UART, and does not employ a virtual serial port.

It is possible that you can P/Invoke the RasHangUp function in rasapi32.dll
to force the release of the port. I have not tried this.

Dick

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.