# Q2687RD download dwl via USB Problem **URL:** \ **Category:** Legacy AirPrime modules\ **Created:** [February 28, 2013, 5:18pm UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190 "2013-02-28T17:18:40Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![ass25](https://avatars.discourse-cdn.com/v4/letter/a/a5b964/32.png) [@ass25](https://forum.sierrawireless.com/u/ass25)\ **Post date:** [February 28, 2013, 5:18pm UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/1 "2013-02-28T17:18:40Z")
We download dwl files via usb to Q2687. but we found problem If I tipe at+cfun=1 or at+wdwl command the com port in windows Down and Up and from this aou terminal program is pause(we use terraterm ) and we need close and open port in terminal. Pls help us to resolve this problem ---
**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.sierrawireless.com/u/awneil)\ **Post date:** [February 28, 2013, 6:49pm UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/2 "2013-02-28T18:49:44Z")
This is an inherent problem with USB, because the device restarts - so the COM port really does go away and come back again. ---
**Author:** ![davidc](https://avatars.discourse-cdn.com/v4/letter/d/a183cd/32.png) [@davidc](https://forum.sierrawireless.com/u/davidc)\ **Post date:** [February 28, 2013, 11:42pm UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/3 "2013-02-28T23:42:58Z")
Hiya, And in Windows if the USB connection goes away while your terminal program is still connected or open, when your USB device re-enumerates it will be given a different COM port number… ciao, Dave ---
**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.sierrawireless.com/u/awneil)\ **Post date:** [March 1, 2013, 8:37am UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/4 "2013-03-01T08:37:38Z")
> [@davidc](#): > > in Windows if the USB connection goes away while your terminal program is still connected or open, when your USB device re-enumerates it will be given a different COM port number… No, that’s not (necessarily) true; in fact, I’ve never seen that happen. When I’ve been using a terminal over a reset of a SiWi USB port, I’ve used the following approach: 1. Issue the AT+CFUN=1 (or whatever) command 2. In the terminal program, disconnect the port 3. Wait for the device to restart and Windows to re-enumerate the port (listen for the sounds and/or watch in Device Manager) 4. In the terminal program, reconnect the port You used to have to do the same thing with TMT - but DS now handles this automatically (or, at least, tries to) I seem to remember that someone posted some PC code to do this automatically at some point… ---
**Author:** ![davidc](https://avatars.discourse-cdn.com/v4/letter/d/a183cd/32.png) [@davidc](https://forum.sierrawireless.com/u/davidc)\ **Post date:** [March 4, 2013, 5:46am UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/5 "2013-03-04T05:46:18Z")
Hiya, > [@awneil](#): > > > [@davidc](#): > > > > in Windows if the USB connection goes away while your terminal program is still connected or open, when your USB device re-enumerates it will be given a different COM port number… > > No, that’s not (necessarily) true; in fact, I’ve never seen that happen. Oops. My apologies. The modem port is NOT re-enumerated when using the Sierra Wireless USB driver. Sorry for the confusion and mis-information 😊 . However, I have seen this when using other serial USB devices … I had issues with a project that used a serial to USB chip that was power cycled when the host CPU was power cycled and ran into the problem I noted above. ciao, Dave ---
**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.sierrawireless.com/u/awneil)\ **Post date:** [March 4, 2013, 8:11am UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/6 "2013-03-04T08:11:38Z")
We may be talking at cross purposes regarding “enumeration”? When the external device is restarted, it is equivalent (as far as the Host is concerned) to unplugging the device, and plugging it back in again - so the Host (Windows, in this case) will “enumerate” it the same as when any device is plugged in. However, when it is plugged back in, the Host’s “enumeration” should recognise it as an “already-known” device - so, in this case, it should re-appear as the same COM port. I’m not a USB expert, so my use of “enumeration” may not be quite right in the above - please excuse me if so… ---
**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.sierrawireless.com/u/awneil)\ **Post date:** [March 4, 2013, 8:17am UTC](https://forum.sierrawireless.com/t/q2687rd-download-dwl-via-usb-problem/6190/7 "2013-03-04T08:17:18Z")
Some people get confused between using the built-in USB on a SiWi device, and a USB-to-Serial converter connected to a UART on a SiWi device: > [@awneil](#): > > When the external device is restarted… In the case of the USB port on a SiWi device, restarting the SiWi device inherently also restarts its USB port. But this is not the case when you use a USB-to-Serial converter connected to a UART on the SiWi device: with this arrangement, the USB-to-Serial converter is not restarted by restarting the SiWi device - so you don’t get these issues.