# STM32 USB/Virtual COM port problems

Last week I successfully could connect my STM32F103C8T6 (aka Blue Pill) with Virtual Com Port. My OS is Windows 10, 64 bit.

In the Ports (COM & LPT) section of Device Drivers, COM8 was shown and I could see my print statements (sent over USB) while running the program (after uploading, disconnecting + reconnecting the USB cable and start putty).

Today I wanted to try it with my (also) STM32F103C8T6, but this is a minimal eval board.

When I plugged it in, I get in the device drivers/Universal Serial Bus Controlelrs:

Unknown USB Device (Device Descriptor Request Failed),


And when clicking on details:

Windows has stopped this device becaue it has reported problems (Code 43)

A request for the USB device descriptor failed.


Than I check on google and found some (very few resources) to reinstall the Virtual Com Port driver (from ST Electronics).

I did that, but since now on both my STM32s (also the blue pill) I get an Unknown USB Device and the COM8 is not showing up anymore.

I use (USB stick like) ST-Link V2 (not V2.1).

Does anybody know how to see my STM32s in the device manager again (also as COM port)?

Side question (but maybe I should post it as separate question): Is it possible to use two STLinks (to two different STM32 devices) at the same time? (preferably with Virtual Com ports)

• @MarcusMüller Yes ... I will add it to the question – Michel Keijzers Aug 20 '17 at 11:01
• You need to implement USB device stack. – P__J__ Aug 20 '17 at 11:05
• @PeterJ ... I initialized the USB port (with STM32CubeMx) ... also the program HAS already worked, so the problem cannot be in the program itself. – Michel Keijzers Aug 20 '17 at 11:09
• @PeterJ STM32CubeMX comes with various middlewares such as: FATFS, FREERTOS, LWIP and USB stack, these are not the part of the HAL indeed, still when configuring USB you can choose to use these middlewares. – Bence Kaulics Aug 20 '17 at 12:15
• @MichelKeijzers Are you sure that your dirvers are installed correctly? It is not enough to install the STM COM port dirver by running the VCP_V1.4.0_Setup. The readme file contains steps that should be done after install. Like running the dpinst_x86.exe for windows 7, 32 bit from the install directory. – Bence Kaulics Aug 20 '17 at 12:17