2.1 UART Validation

Before I start writing some code that communicates over the Universal Synchronous Asynchronous Receiver Transmitter (USART) peripheral, I need to validate that I have working hardware and software tools.

Board Connectivity

Even if the peripheral is capable of doing synchronous communication (that’s the S in USART), asynchronous communication (that’s the A) which only needs 3 wires (GND, TX, RX, (no clock)) is usually what is needed in non specialized cases.

Boards sold online often have dedicated pre-soldered pins for UART connectivity similar to what I have seen before for the SWD interface. The VCC-GND board I used previously doesn’t have such dedicated pins but the functionality is wired on the pins PA9 (TX) and PA10 (RX).

I will use a board with dedicated pins (GND, TX, RX, VCC 3.3V). Board specifications can be found here.

STM32F030F4-V2.00

USB to UART adapter

An adapter is needed to connect to a PC. Either due to difference in voltage (RS232) or serial protocol (USB). Pins PA9 and PA10 are 5V tolerant, so you could interface an Arduino Uno to a STM32 board to use it as a USB to serial adapter if you happen to have a spare Arduino Uno.

I use an adapter based on Silicon Labs CP2102 chipset. Windows has USB driver available for Silicon Labs CP210x chipset family. The adapter enumerates as COM4 on my Windows PC.

I connect the adapter to the board to provide 3.3V and make sure to cross RX and TX wires (STM32 RX <-> Adapter TX, STM32 TX <-> Adapter RX).

STM32 Cube Programmer UART connection

So far I have been using the ST-Link interface with STM32 Cube Programmer to flash and debug. The application also support the UART interface.

Embedded Boot Loader

A reset of the board while jumper BOOT0 is removed will select the System memory instead of the flash memory for execution. This is where the serial flash loader protocol is implemented on chipset side.

BOOT0 Jumper Selection

Testing

The checklist goes like this:

Board connected to USB adapter
USB driver installed on Windows PC
USB adapter plugged in and enumerates as a COM port
STM32 Cube Programmer list the COM port in device selection menu
BOOT0 jumper removed and board reset to start the embedded flash loader.
Board flash memory can be erased, written or read with the programmer.

Checkpoint

I have now working hardware and software that communicate through the serial link.

Next, I will make sure the code I wrote so far is working on the new board.