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Com ports in use?

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Old 09-16-2004, 12:52 PM
pjs2004 Offline
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Com ports in use?

Does anyone know of a utility for Windows XP that tells you what com ports (virtual com ports incuded) are in use and what software/hardware is using them?

Here is backgound info for my question...kinda long:

I have a Windows XP Professional SP1 laptop that I am trying to configure for bluetooth so that I can use Activesync with my Ipaq pocket pc. I have searched for and found out how to set this up, so I know the exact procedure. However, in following the procedure, I need to set my Activesync software to the com port that the bluetooth device is using. The problem is that the bluetooth device is using virtual com port 38 (shown in the bluetooth software) and the Activesync software requires that it use a com port in the 1 - 9 range. All this is well known to be the way it has to be set up, so I don't have an issue with that. I just need to be able to get the bluetooth device on a com port in the 1 - 9 range. The only way to do that is to uninstall whatever is taking up the other com ports and then reinstall the bluetooth device.

The only way I can determine what com ports are in use, is to go to my modem properties and look at the port configuration. The drop down list shows all the com ports (hardware and virtual) from 1 - 256. Every port, except 2 and 3, from 1 - 37 is "in use." For some reason, the bluetooth device will only use a virtual com port because it will not use 2 or 3. It always uses the next virtual port that is not "in use" -- in this case, 38.

Sorry for the long explanation. The problem comes down to being able to uninstall whatever is using all those com ports (1 - 37, except 2 and 3). If I am able to do this and then reinstall the bluetooth device, the bluetooth device will take one that I can use with Activesync (1 - 9). I have tried uninstalling various things in device manager, but I have no way of knowing if any of the things I am uninstalling is using a com port, except for the modem, of course.

I cannot find out what is using all these com ports, and I could not find any utility that would identify what is using the com ports that are "in use." If I knew that, I could simply unistall that hardware/software.

Any help is much appreciated.

Last edited by pjs2004 : 09-16-2004 at 01:08 PM.
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Old 09-16-2004, 01:40 PM
bbeard67 Offline
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Join Date: Aug 2004
Posts: 433
Go into Device Manager and expand Ports

open "My Bluetooth Places" (from the Stat Menu or the System tray) on the PC. From the Bluetooth Menu choose Advanced Configuration. Select the Local Services Tab and note the COM port assigned to "Bluetooth Serial Port"

Now in ActiveSync on the PC from the File menu choose Connection Settings. Make sure the first check box is ticked, stating "Allow serial cable or infrared connection on this COM port". From the drop down list under this check box - select the COM port you noted previously (from the Bluetooth Local Services Tab).

It could also be that your Firewall is blocking the ports
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Old 09-16-2004, 02:00 PM
pjs2004 Offline
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Join Date: Sep 2004
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Thanks for the reply. I found the same procedure you described in the bluetooth forums. The problem is that the COM port in the "Local Services" tab is 38, and the Activesync software requires the port to be in the range of 1 - 9 (as noted from others having this problem). So, COM 38 is not listed in that drop down list.

I need to be able to move the bluetooth device to a COM port in the 1 - 9 range, but first I have to find out what is using these ports so that I can uninstall that hardware/software. Is there a utility that will tell me what is using these (or all) COM ports?
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Old 01-25-2008, 02:56 PM
hickdog Offline
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Solution for freeing COM ports in use.

I had exactly this problem myself. I found a link to this site by searching on "find com ports in use" on google. It describes selecting the com port under Ports in device manager, right-clicking for properties, then clicking "advanced" on the Port setting tab. There is a "Port" dropdown that lists all the ports, and shows loads of them used. to free a port, select the port you want (even if it says used), and click through the "port in use" dialog and then click okay on the main dialog. Then select Action->scan for hardware changes on the Device Manager tool bar. Now when you add a serial bluetooth port, you should be able to select the port you freed.
I determined what I could free by doing this same step for all the modem devices listed in device manager to see what ports they were using.

Good Luck
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Old 02-12-2008, 12:12 PM
pelesl Offline
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Join Date: Feb 2008
Posts: 3
I have a solution

So I had the same problem. I'm using devices with the FTDI usb to serial chip, and various other USB to serial converters. I had to recently reinstall windows due to a problem with winlogon.exe consuming 100% CPU (never found a solution, but I did correlate it with my computer no longer synchronizing files with the domain controller). After the reinstall, plugging in my FTDI device sent it to COM17, and if I went into its properties in device manager to change the COM port, everything from 3 to 17 said "in use".

I tried the trick of forcing the device to use these "occupied" ports, which certainly clears the "in use" flag but does not actually delete these non-existent ports. Using portmon, all these ports would still show up. What's more, I had two COM3's, one of which was my FTDI device (which, in device manager, showed up as COM2) and no COM2. The same list of COM ports could be replicated in a .NET program I'm writing to communicate with serial ports (which just asks windows for all serial ports available to make a list). Interestingly, a call to this function normally shows the COM ports in numerical order, but I had a second COM1 and COM3 after the list of COM1 through COM17.

Using FTDI's FTClean utility, which I think is supposed to clear up this issue of ever increasing COM port numbers, didn't do anything. I ran it several times, rebooted, etc., to no avail.

If you go to the portmon page (linked above), they explain that portmon goes to the registry to find COM ports. So I went to the registry key they mention (HKEY_LOCAL_MACHINE\Hardware\DeviceMap\SerialComm) and deleted everything that wasn't COM1 (mapped to \Device\Serial0) and COM3 (mapped to \Device\VCP0, which is the FTDI device). I didn't have to reboot or log out and log back in; changes took effect immediately, and this removed all the fake ports (they were all mapped to \Device|vcomxx, where xx was a number).

While I'm at it, if you want to learn a lot about serial port programming in .NET, check out this link. How about that nightmare of COM ports disappearing forever in windows Vista?
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Old 02-12-2008, 01:24 PM
pelesl Offline
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Join Date: Feb 2008
Posts: 3
Spoke too soon...

I may have spoken too soon.... I rebooted and COMs 1-16 were listed, 2-16 which were the fake "vcom" variety. The FTDI device, which is COM3 in the device manager, doesn't show up in the registry list, but it does show up in my .NET program, and I can access it just fine.

More as I get it....
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Old 02-12-2008, 05:47 PM
pelesl Offline
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Join Date: Feb 2008
Posts: 3
Windows Mobile Development Kit

In my case these virtual com ports may be from the Windows Mobile Development Kit 6, which apparently requires 14 virtual com ports to do cell phone emulation....

Searching the registry, I eventually ran across entries for XPVCOM devices, and I believe these must be the COM ports I was seeing.

So in my case, I guess I have to live with it....
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