Which pins does STM32F03 use for USART?
This is how to determine the UART pins, assuming you have a STM32F030R8Tx in a LQFP64 package:
Open the datasheet on go to Table 8. STM32F0x0 USART implementation. It lists what USARTs the chip has. In this particular case: USART1 and USART2.

All the Pxx pins are GPIO pins by default. USART features can be routed to them using the alternate functions. So the easiest way to determine the USART pins, is to check Table 12. Alternate functions selected through GPIOA_AFR registers for port A and the following tables.


If you search for &quot;USART1&quot; and check for the (2) marker, you'll find:

TX: PA2, PA9, PA14, PB6
RX: PA3, PA10, PA15, PB7
CTS: PA0, PA11
RTS: PA1, PA12
CK: PA4, PA8

You'll find similar results for USART2. You will need to configure the pins alternate function in order to route USART signals to the desired pin. Each USART function (RX, TX etc.) can go to 2 to 4 different pins.
Additional pin information can be found in *Table 11. STM32F030x4/6/8/C pin definitions.