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Which COM Port Numbers Were Assigned to Each of the Physical Ports on My NI-Serial Card

Hardware: Serial

I have one or more PCI or PXI Serial cards installed on my computer. I can see all of the COM ports listed in MAX, but I can't tell which COM port corresponds to a particular physical port number on each of my cards. For example, I have a PXI-8420/8 and a PXI-8421/4, giving me a total of 14 COM ports (including the two that are built-in with the PXI controller). I don't want to have to use trial and error to figure out which of the connectors I should use if I want to communicate with COM3.

In most cases, COM port numbers will be assigned sequentially beginning with the first COM port number that is available. If you only had the PXI-8421/4, then port one on the board would most likely be COM3, and port 4 would be COM6. When you have multiple boards, it may be difficult to know for sure.

To find the mapping of physical ports to COM ports, open the Device Manager. You can do this by right-clicking on My Computer (on the desktop), then going to Properties. Click on the Hardware tab, then choose Device Manager. There you should see a listing of the individual ports.

From MAX you can clear the unused COM ports in order to reallocate them and configure them to new settings. This is done by going to NI MAX selecting Tools»NI-Serial»Recover Unused COM Numbers. This clears the Windows registry of all ports that are not currently connected.

Figure 1: Configuration in MAX (Tools»NI-Serial»Recover Unused COM Numbers)

Related Links:
Products and Services: USB Serial Interfaces
Knowledgebase 2MRAP77N: Making unused COM Ports available in Windows
KnowledgeBase 4R69QEYW: How Are the COM Ports for My USB Serial Device Assigned?


Report Date: 04/23/2003
Last Updated: 02/15/2017
Document ID: 2WM8JL0Q

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