rod palmer

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5 years, 9 months ago.

UART2 and 3 on the L432KC

the chip https://www.st.com/en/microcontrollers/stm32l432kc.html has 3 uarts but the NUCLEO board appears to only have 1 functional uart.

the second one is only half implemented (commented out in the PeripheralPins.c ) and the 3rd one is not mentioned at all.

I am very new to ARM and the mbed environment, is there anything I can do about this ?

Question relating to:

Last updated: 16 Nov 2020
Affordable and flexible platform to ease prototyping using a STM32L432KCU6 microcontroller.

Thanks to both of you. Much appreciated.

posted by rod palmer 26 Jul 2018

1 Answer

Jenny Plunkett
5 years, 9 months ago.

Hi Rod,

I took a look at the datasheet for the STM32L432KC board here: https://www.st.com/resource/en/datasheet/stm32l432kc.pdf

It looks like this board has a USART1, USART2, and an LPUART1. However, according to the board's PeripheralPins.c file in Mbed OS and the datasheet I listed above, the LPUART TX and RX use the same pins as the USART2 TX and RX. So the board has the following USART's available within Mbed OS by default:

  • USART1: TX = PA_9 or PB_6, RX = PA_10 or PB_7
  • USART2 (connected to STDIO): TX = PA_2, RX = PA_15

If you would like to use the LPUART instead of USART2, I would try changing the lines that are commented out in the PeripheralPins.c file to the following:

MBED_WEAK const PinMap PinMap_UART_TX[] = {
//  {PA_2,       UART_2,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART2)}, // Connected to STDIO_UART_TX
    {PA_2,       LPUART_1,STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF8_LPUART1)}, // Connected to STDIO_UART_TX
    {PA_9,       UART_1,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART1)},
    {PB_6,       UART_1,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART1)},
    {NC, NC, 0}
};

MBED_WEAK const PinMap PinMap_UART_RX[] = {
//  {PA_3,       UART_2,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART2)},
    {PA_3,       LPUART_1,STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF8_LPUART1)}, // No LPUART_1 TX
    {PA_10,      UART_1,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART1)},
    {PA_15,      UART_2,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_USART2)}, // Connected to STDIO_UART_RX
    {PB_7,       UART_1,  STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART1)},
    {NC, NC, 0}
};

And then you can use the following Serial object within your application code for the LPUART: Serial serial_object(PA_2, PA_3); //TX, RX

Please let me know if you have any questions!

- Jenny, team Mbed

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Accepted Answer