UART is acronym for Universal Asynchronous Receiver – Transmitter. STM32F103C8T6 UART is the TTL serial, the TTL limit signal between 0V - Vcc. If MCU working on 3.3V, TTL limit will be 0V - 3.3V The COM port (RS232) on PC working on -13V to +13V level, so you can not directly connect your STM32F103C8T6 UART to the COM port. You must use the RS232 to TTL device to connect your MCU to the PC. The following image is a RS232 to TTL device Or you can use a USB to TTL serial (FT232RL) like the following In this article we use the blue pill board. We also need a ST-LINK V2 programmer There are 3 UART ports available on STM32F103C8T6 Tx is the transmitter, Rx is the receiver. Tx must connect to Rx and vice versa. Here is the list of materials that we need Hardware: FT232RL, Blue pill board, and stlink v2 mini programmer. Software: Atollic TrueSTUDIO ( https://atollic.com/truestudio ). STM32CubeMX ( https://www.st.com/en/development-tools/stm32cubemx.html ). STM