STM32 Virtual COM port, usb device not recognized ''unknown device''

[nemoczech]

Posted on July 24, 2014 at 04:59

Hello,

I'm working on realizing virtual com port on STM32L151 board. After I plug it into PC via usb, there are messages saying ''usb device not recognized''. I look into computer -- properties -- device manager, it is a ''unknown device'' and can't be recognized as com port.I have installed virtual com port driver x64 provided by ST (I'm working on Windows 7 64 bits). Does anyone have experienced similar things?How should I fix it?Thanks forward.Jingyu   #usb #stm32l #driver

[chen]

Posted on July 24, 2014 at 10:21

Hi

Yes, I had the same thing. My problem was the USB peripheral was being clocked at the wrong freq. (peripheral clocks set up wrong). If that is not your problem, you will have to analyse the enumeration of the device on the PC.

[pradeepa]

Posted on July 25, 2014 at 12:36

You can go to device manager and goto device properties for you unknown device. Then check the hardware IDs and see whether correct PID/VID values are there. I guess the values will not be there. If not your USB device descriptor has not come to the PC. That means firmware did not respond to standard USB device requests. That can be one of many reasons. Common things could be clock configuration issues or errors in device descriptors. 

Try ST VCP example and check whether it is working.