VB6 MSComm, ports above 127 return 8002

Question

I have a simple function that checks if we have open ports on the system, I would test ports from 1 to 256. For some odd reason when I have device at port over 127 system returns error 8002. This is very odd because when I use a different C++ application to check connection device is found and is available for reading.

This issue is related to the MSComm32.OCX, which has a limit on how many ports are available. I need to increase this limit to 256. I found a list of instruction below, but I wasn't able to find "3D 10 00" in the MSComm32.OCX file, this was on Windows 8 PC. However, on Windows XP MSComm32.OCX did contain "3D 10 00", i quickly found the string and added a new byte "FF" and deleted byte "10" using http://mh-nexus.de/en/hxd/ and saved it as a new file.

First you copy the file MSCOMM32.OCX to a safe place.
1. Obtain a HEX editor.
2. Open de file MSCOMM32.OCX
3. Find the string "3D 10 00"
4. There should be only one. This string is unique.
5. Change the string to "3D FF 00"
6. Save the file.

Your using an "edited" version of the OCX? as by default the upper port number limit is 16 — Alex K., Apr 14 '15 at 10:50
Ah sorry, forgot to mention, application is running on Windows — Vlad Vladimir Hercules, Apr 14 '15 at 11:09
I understand now on what you mean by OCX, is their a way to increase this limit? — Vlad Vladimir Hercules, Apr 14 '15 at 13:49
I have tried : First you copy the file MSCOMM32.OCX to a safe place. 1. Obtain a HEX editor. 2. Open de file MSCOMM32.OCX 3. Find the string "3D 10 00" 4. There should be only one. This string is unique. 5. Change the string to "3D FF 00" 6. Save the file. And unable to find "3D 10 00" in my OCX file on WIndows 8 — Vlad Vladimir Hercules, Apr 14 '15 at 14:15

score 0 · Answer 1 · answered Mar 16 '21 at 23:47

I don't know if this will help in your case, but you will be unable to edit the original ocx file using this procedure. You can only edit the file after it has been registered. The original is the "cookie cutter" from which all registered files are descended and it has a completely different structure. The registered file will have the "3D 10 00" sequence in it and can be modified. It would be nice if the original could be modified since all new instances would then have the modified upper port limit already in them, but Microsoft made sure that won't work.

VB6 MSComm, ports above 127 return 8002

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