ID #1088

How to operate COM10 to COM256 in Windows?

This question is very old, and should be answered and solved in today software since a long time. Surprisingly this comes up again from time to time. So here is the classic answer, digged up from the old FAQ.

Very frequently Windows programs refuse to operate with COM10 or higher. What is the reason?

  1. The program is an old 16-bit application. In this case COM9 is the highest available interface.
    It is very likely this is not the cause today, but you never know.
  2. The program offers a list of ports, only containing COM1 through COM9.
    Please contact the programmer. This is a limit imposed by his application.
  3. The program does not open the port in the correct way, please contact the programmer.
    Probably a name like "COM11:" is used to select the port. This is not allowed. The correct name is "\\.\COM11", i.e. with <Backslash><Backslash><Dot><Backslash> as prefix; further the colon at the end is not allowed. This method also operates with COM1 through COM9.

Programmers shall check the MSDN article about this problem.

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Last update: 2011-12-21 16:48
Author: Support
Revision: 1.0

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