How to enable serial-USB on B-L475E-IOT01A1 board?

[Ravi.N]

I'm using the STM32 Io T discovery board (B-L475E-IOT01A1) to learn micro-ROS since this is a supported board with a demo use case.

To flash the firmware on the board, the JP4 connector was set to 5V_ST_LINK pin and flashing was successful.

The board after flashing (re connection) should post few topics on the serial USB port. I tried connecting the ST LINK USB port to the PC and with the jumper JP4 set to 5V_USB_FS and to 5V_ST_LINK pins in separate exercises. In both case, the port is visible as ST LINK port on the PC and not as SERIAL-USB port. Therefore I'm not seeing any output from the board to the PC.

Is there any additional jumper setting to be done while JP4 connected to other pins except 5V_STLINK to enable SERIAL-USB on the STLINK port?

[Peter BENSCH]

Welcome, @Ravi.N​, to the community!

With JP4 you select where the 5V come from, from which the board generates the internally required voltages (e.g. 3.3V for the VDD of the STM32L475). So when you connect the board

• via USB of the ST-LINK: JP4 = 5V_ST_LINK
• via the Arduino power pin: JP4 = 5V_ARD
• via CN9 (USB OTG): JP4 = 5V_USB_FS
• via CN7: JP4 = 5V_USB_CHARGER

What you probably mean by SERIAL-USB is the so-called Virtual COM Port (VCP), which is provided by the ST-LINK. For this purpose, the ST-LINK inserts the signals of the RX/TX lines of the STM32L475 into the USB data stream.

In order to be able to see the VCP, some requirements have to be met: the firmware of the ST-LINK should be up to date (check with STM32CubeProgrammer) and the JP4 should be set to 5V_ST_LINK, alternatively to 5V_USB_CHARGER. Of course, you can only see data via the VCP if the STM32L475 program outputs data via the corresponding UART.

Regards

/Peter