COM number changing whenever the modem restarts??

Hi all, I am running Windows 7 Pro and a FXT009 modem using the Version USB drivers.

Using developer studio (2.3.2 and 3.2) I am unable to update the application on the modem as when the AT+WDWL command is used (by DS) the modem restart and developer studio never finds it as it has been re-enumerated. i.e. It was on COM1 then it restarts now it is on COM2 and so it continues until it reached the end of the defined range and then it no longer works (the driver that is) the modem is still operating as normal.

I have also noticed this behavior if the modem restarts due to an exception. I am able to flash the mode using tera term and the UART. But I am unable to develop and debug the application when the COM port keeps changing…

PS It might be worth noting that Windows sees the device having the same COM port (in this case 7) continuous. The point at which the Sierra Wireless enumerated COM numbers are depleted, device manager reports the device as not being able to start (but still has COM7 assigned). So I assume the device can’t start because the driver wants (for some unknown reason) to assign a new COM number to the modem, but there are none available (as defined by the “USB driver configuration” tool)

Any help would be greatly appreciated as I am now stumped.



I am not able to reproduce the issue at my end on Windows7 with driver version
Could you please provide us the exact steps to reproduce the issue?
Also can you try on another windows machine and see whether you are able to download the FW on FXT009.

Please share the USB driver version by right click on "Control Panel -> Device Manager -> Modems -> properties -> Driver -> Driver details "


Hi Rex-alex. Thanks for your reply. The driver details are as follows

On the driver page I get the below:

Driver Provider: Sierra Wireless
Driver Date: 14/02/2012
Driver Version:

On the driver detail page I get the below:

Driver file: C:\Windows\system32\DRIVERS\SierraUsbPort.sys
Provider: Not available
Date: Not available
Digital signer: Not digitally signed


  1. I installed the drivers…
  2. I plugged in the modem
  3. The modem is detected and drivers installed
  4. I leave the USBconfig setting default i.e. COM1 - COM2
  5. I open DS and connect to the modem.
  6. I can see all traces and device information
  7. As soon as I cause the modem to restart, by wanting to download firmware DS hangs at “Waiting for module detection”
  8. Hitting “Refresh available ports” shows a new port being available.
  9. Opening and connecting to that port repeats the above cycle.
  10. However “Refershing available ports” does not show a new port as the allowed range (COM1 - COM2) has been saturated
  11. Had the range been COM1 to COM100, I would have been able to repeat the above cycle until I reached COM100…

I hope that helps… I will try and connect from a another computer and report back.



I just tried this on another machine. DS with the same driver details shown in my previous post. The download work fine.

Both machine are 64bit…

Any ideas?



Could you please share the details of the machine in which download works fine.

Also please share the driver details by right click on "Control Panel -> Device Manager -> Modems -> properties -> Driver -> Driver details "


The driver details are the same as for the other. See previous posts.

Not sure what details you want of the PCs. Let me know I will provide them… but they are both laptops running Win7 Prof SP1 64bit

Any other ideas anyone?

Is there a way to completely remove the driver and all related settings from the PC. i.e. to make sure there is nothing and try a fresh install of the drivers in case something went wrong…



Yes this is a good idea. You can uninstall the previous USB driver installed and other USB drivers if any. to do so go to control panel -> right click on the driver which you want to uninstall and uninstall the drivers.

Then install the driver version It is recommended to restart the PC after the installation.

Let me know if you are facing the issue after this also.


Does this clear any registry entries / settings?

no… I don’t think so…


Is there a recommended way of clearing all that out as well?

I didn’t get your point. Why you want to clear registry settings?

Because this is a strange behaviour I want to remove everything from my PC as if I never installed the driver. Then I want to try and reinstall it to see if that resolves the issue. Just removing the driver may leave registry settings which are causing the problem. So I would like to remove everything from my PC related to the USB driver… files/ registry and anything else.

Is there a way to do that?



for changing the registry settings you can search in Microsoft Windows support section.
Hope below link will help you:
Meantime did you try uninstalling the existing drivers and reinstalling the Is it working now??