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Why do comm port numbers change?


@teslac wrote:

I know Im replying to myself but I wanted to put this out there that I found the issue.  The problem is with the BIOS and the numeric reassignment of ports happens on re-boot and is a know problem.  NI has a tool for port configuration.exe or simply changing the port assignments in MAX to a specific name will also fix this problem.


Intresting... I have a system with  rs232 ports and 6 power supplies with USB-rs232 built in making 12 total serial ports in one PC.

 

The hardware port are PCIe cards with two serial ports on them. I struggles with a simmilar issue for a while but I found if I installed the cards one at a time with a reboot between each one. They would fall in line (First card Com1 and Com2, second card Com3 and Com4, third card Com5 and Com6) and stay that way from there on out. None of these ports has been ever been moved to another com port number.

 

The 6 power supplies are a different story. They have USB connectivity but that is really a USB-rs 232 converter inside and they show up as com ports. Windows 7 would occasionally rearrange them. I found that if did this when I just hit all the power switchs quickly in a row. But if I start at the first one and turn it on, wait for Windows to detect it before moving on to the next each power supply would always return to the same com port. But since I know what power supply is part of which system (6 different systems)  I made a  VI that checks the serial numbers of each power supply and makes adjustments in the VISA settings to set the proper unit on the proper com port just in case they swap again.

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