Title: How to Access Serial Ports Greater Than COM9 Using C/C++
Date: August 4, 1998
KDB: KDB-227
Revision: 0.00
Author: Support
Distribution: External
The following is a tech note published by Microsoft, regarding a solution to accessing com ports above Com 9.
HOW TO: Specify Serial Ports Larger than COM9
Last reviewed: January 20, 1997
Article ID: Q115831
The information in this article applies to:
- Microsoft Win32 Application Programming Interface (API) included with:
- Microsoft Windows NT versions 3.1, 3.5, 3.51, 4.0
- Microsoft Windows 95 version 4.0
CreateFile() can be used to get a handle to a serial port. The “Win32 Programmer’s Reference” entry for “CreateFile()” mentions that the share mode must be 0, the create parameter must be OPEN_EXISTING, and the template must be NULL.
CreateFile() is successful when you use “COM1” through “COM9” for the name of the file; however, the message “INVALID_HANDLE_VALUE” is returned if you use “COM10” or greater.
If the name of the port is \\.\COM10, the correct way to specify the serial port in a call to CreateFile() is as follows:
CreateFile(
“\\\\.\\COM10”, // address of name of the communications device
fdwAccess, // access (read-write) mode
0, // share mode
NULL, // address of security descriptor
OPEN_EXISTING, // how to create
0, // file attributes
NULL // handle of file with attributes to copy
);
NOTES: This syntax also works for ports COM1 through COM9. Certain boards will let you choose the port names yourself. This syntax works for those names as well.
Additional reference words: 3.10 3.50 4.00 95
KBCategory: kbprg kbhowto
KBSubcategory: BseCommapi
Last reviewed: January 20, 1997
© 1998 Microsoft Corporation. All rights reserved. Terms of Use.
End of KDB-227