COM PORTS in XP

[G0AOZ]

Installed a USB to SERIAL convertor on a laptop running XP Pro. Device Manager informs me that it's been allocated COM5. When I look down my list of devices I see COM1 and COM3. The former is the only physical port available on the back of the machine, and the latter is the internal 56K modem. Can't see where COM2 and COM4 have gone...

No hidden devices, and when I run CHANGE PORT it only lists COMMs 1,3 and 5. How can I find out what has snaffled COMMs 2 and 4?

ROGER - G0AOZ.

 

[biglebowski]

Do you have blutooth and a modem installed if so these will probably be using the com ports.

When I was born I was so suprised I didn't talk for 18 months

 

[G0AOZ]

No bluetooth, and the only modem is as per my post above (COM3).

If I go to either of the two devices listed against COM PORTS in Device Manager, and select Advanced options, and then COM PORT, it tells me COMMs 2 and 4 are in use. By what, I have no idea...

ROGER - G0AOZ.

 

[linney]

Frequently a choice has to be made between COM1: and COM3: and between COM2: and COM4: since control lines and addresses are shared. A manufacturer's hardware reference is usually needed to determine the exact settings for a given situation.

"If you are using a serial mouse on COM1 and you have an internal modem on COM3, this configuration may not work because the mouse is using the interrupt that COM3 wants to share. This behavior also occurs if you are using a serial mouse on COM2 and want to use an internal modem on COM4. This configuration is more likely to work on machines that allow for IRQ sharing (such as Micro Channel Architecture [MCA] computers)".

If COM3 is required, it should be reconfigured at the board level to use a different interrupt that is free, such as IRQ 5.

Troubleshooting Serial Port Problems in Windows

http://support.microsoft.com/default.aspx?scid=kb;en-us;105940&FR=1&PA=1&SD=HSCH

Available switch options for the Windows XP and the Windows Server 2003 Boot.ini files

http://support.microsoft.com/default.aspx?scid=kb;en-us;833721&FR=1&PA=1&SD=HSCH

Overview of the COMDisable Tool

http://support.microsoft.com/default.aspx?scid=kb;en-us;819036&FR=1&PA=1&SD=HSCH

See if these lead anywhere?

HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports

Search the Registry for COMn (n = number) and see what else you can turn up.

 

[G0AOZ]

Some interesting stuff in there Linney - many thanks. Will take another look at this problem when I next have the machine in front of me...

ROGER - G0AOZ.