Changing Your Modem

Changing Your Modem’s COM Port Manually

Many times reinstalling an existing modem or replacing and old modem with a new one will lead to problems with the Communications (COM) Port assignment being incorrect for the modem. Most hardware systems will try and assign the modem to COM 1, 2, 3 or 4 as higher number assignments are only available within the Windows interface. Most motherboard Bios’ would prefer the modem to be on COM 1 or 2 (1 and 3 are shared as are 2 and 4), but if the modem comes pre-configured for COM 3 or 4 and there are no jumpers on the modem to reset it to 1 or 2, this causes a problem in Windows, as Windows may not be able to juggle the COM port setting. We’ve seen technicians literally turn themselves inside out removing and reinstalling the modem in Windows Device Manager, only to hit a brick wall when either Windows or the modem fails to cooperate. There is an easier and less frustrating way to handle this though, and that is to edit the Windows Registry to reflect the desired port assignment.

Warning: This procedure involves the editing of the Windows Registry. Anything that involves editing the Windows Registry, if done incorrectly, could render your Windows operating system inoperable, therefore always make a backup of the registry before performing any edits.

  1. Go to Start, Run, and type REGEDIT, then click on OK. This will bring up the Registry Editor.

  2. Click on “+” to the left HKEY_LOCAL_MACHINE to expand it.

  3. Now click on the “+” to the left of the ENUM key to expand it.

  4. Now click on the “+” to the left of the PCI key to expand it.

  5. Now click on the “+” to the left of the VEN_11C1&DEV_xxxxxxx key to expand that.

  6. Now you should see a key called: BUS_00&DEVxxxx

  7. Click on the key (word) BUS_00&DEVxxxx once to highlight it.

  8. In the right pane of the registry editor you will see all of the ID information and settings for the modem.

  9. Now look for the entry called: PORTNAME.

  10. To the right of PORTNAME will be the current COM port assignment.

  11. Right click on the word “PORTNAME” to bring up the popup menu to edit the setting and select modify.

  12. This will bring up another popup window to enable you to change this port setting. In the top of this second menu will be the data “Value Name” and beneath that will be the “Value Data” value to change.

  13. Now just click on COMx entry and change the number “x” to whatever COM port number you want (as long as that COM port is NOT already in use by a physical serial port or another internal modem).

  14. Once you’ve made the change, click OK and exit the Registry Editor.

  15. Now restart your computer and you should be all set.

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