Because my l053 board has some problems, I cannot use the mbed serial port to debug the program.
Therefore, you can connect to your computer only by connecting to the serial port module.
What's more, the Tx and Rx pins on the nucleus Board are not connected to the MCU by default ......
To use two pins, connect sb62 and sb63 on the back of the Board (solder ).
This is explained in the document given by St. There are many related documents below this webpage. The PDF of um1724 is detailed.
“The USART2 interface available on PA2 and PA3 of the STM32 microcontroller can be connected to ST-LINK MCU, STMicroelectronics Morpho connector or to Arduino connector. The choice can be changed by setting the related solder bridges. By default the USART2 communication between the target MCU and ST-LINK MCU is enabled in order to support Virtual Com Port for mbed (SB13 and SB14 ON, SB62 and SB63 OFF). If the communication between the target MCU PA2 (D1) or PA3 (D0) and shield or extension board is required, SB62 and SB63 should be ON, SB13 and SB14 should be OFF. In such case it possible to connect another USART to ST-LINK MCU using flying wires between Morpho connector and CN3.”
Method for debugging external serial port of the St nucleus Board