# HL7648 USB connect/disconnects

**URL:** <https://forum.sierrawireless.com/t/hl7648-usb-connect-disconnects/14392>\
**Category:** Legacy HL Series\
**Created:** [November 8, 2018, 12:01am UTC](https://forum.sierrawireless.com/t/hl7648-usb-connect-disconnects/14392 "2018-11-08T00:01:22Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![mmalopy](https://avatars.discourse-cdn.com/v4/letter/m/4da419/32.png) [@mmalopy](https://forum.sierrawireless.com/u/mmalopy)\
**Post date:** [November 8, 2018, 12:01am UTC](https://forum.sierrawireless.com/t/hl7648-usb-connect-disconnects/14392/1 "2018-11-08T00:01:22Z")

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Hello all,  
I’m bringing up a HL7648 based solution/drop-in replacement connected with a RPi3 over a USB-to-serial connection. However, I am observing continuous USB connects/disconnects every 6 seconds with the same product/manufacturing information (which I am guessing is the HL fsbl):  
[109.803796] usb 1-1.4: new high-speed USB device number 4 using dwc\_otg  
[109.935011] usb 1-1.4: New USB device found, idVendor=8087, idProduct=0716  
[109.935024] usb 1-1.4: New USB device strings: Mfr=0, Product=0, SerialNumber=0  
[113.856125] usb 1-1.4: USB disconnect, device number 4  
[116.963896] usb 1-1.4: new high-speed USB device number 5 using dwc\_otg  
[117.095119] usb 1-1.4: New USB device found, idVendor=8087, idProduct=0716  
[117.095133] usb 1-1.4: New USB device strings: Mfr=0, Product=0, SerialNumber=0  
[120.000130] usb 1-1.4: USB disconnect, device number 5

On a different prototype board with the same linux kernel distribution and Sierra wireless module, I get the same initial USB connect/disconnect pattern the first time followed by a second USB iteration where it correctly identifies itself as a sierra wireless module that I am attempting to interface with:  
[397.404111] usb 1-1.4: new high-speed USB device number 7 using dwc\_otg  
[397.535336] usb 1-1.4: New USB device found, idVendor=8087, idProduct=0716  
[397.535350] usb 1-1.4: New USB device strings: Mfr=0, Product=0, SerialNumber=0  
[400.440473] usb 1-1.4: USB disconnect, device number 7  
[403.554056] usb 1-1.4: new high-speed USB device number 8 using dwc\_otg  
[403.696948] usb 1-1.4: New USB device found, idVendor=1519, idProduct=0443  
[403.696963] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3  
[403.696971] usb 1-1.4: Product: SWIMCB71XX  
[403.696979] usb 1-1.4: Manufacturer: Sierra Wireless Inc.  
[403.696986] usb 1-1.4: SerialNumber: 014697000056835  
[403.732254] cdc\_acm 1-1.4:1.0: ttyACM0: USB ACM device  
[403.735762] cdc\_acm 1-1.4:1.2: ttyACM1: USB ACM device  
[403.738892] cdc\_acm 1-1.4:1.4: ttyACM2: USB ACM device

Does anyone recognize this behavior? Is it a possible clue on what component or configuration may be preventing the module from successfully registering itself over USB with the Linux kernel as a Sierra Wireless device?

Thanks for any input…  
Mark M

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**Author:** ![Sierra\_klin1](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@Sierra\_klin1](https://forum.sierrawireless.com/u/Sierra_klin1)\
**Post date:** [November 9, 2018, 8:25am UTC](https://forum.sierrawireless.com/t/hl7648-usb-connect-disconnects/14392/2 "2018-11-09T08:25:51Z")

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Hi Mark ,  
It seems your module does not start up or always reboots. (VID/PID USB: 8087/0716 is for Flash download. 1519/0443 is for normal mode).  
Pleases check first with your power supply.

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**Author:** ![mmalopy](https://avatars.discourse-cdn.com/v4/letter/m/4da419/32.png) [@mmalopy](https://forum.sierrawireless.com/u/mmalopy)\
**Post date:** [November 12, 2018, 11:10pm UTC](https://forum.sierrawireless.com/t/hl7648-usb-connect-disconnects/14392/3 "2018-11-12T23:10:54Z")

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Thanks,  
We had an issue with Vref - it was toggling on/off with the state of the POWER\_ON\_OFF control I/o - having Vref held static at the desired voltage value certainly helps.

Mark M

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**Author:** ![rakeshsafir](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/rakeshsafir/32/4412_2.png) [@rakeshsafir](https://forum.sierrawireless.com/u/rakeshsafir)\
**Post date:** [April 20, 2019, 3:29am UTC](https://forum.sierrawireless.com/t/hl7648-usb-connect-disconnects/14392/4 "2019-04-20T03:29:04Z")

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Hi @mmalopy @Sierra_klin1

Can you share a bit more detail of how did you resolve this. I’m facing the same issue that the USB modem stays in download mode with a USB VID:PID as 8087:0716

Rakesh