Using custom RX/TX UART pins on nrf51822

Question

Hi, 
 I have developed an application on an nrf51dk, with SDK12.3 (as it was the latest that I could make it work with). It is running fine on the DK, but when moving to the custom pcb i ran into a few problems, one of them being that the DK uses pins TX=P0.09 and RX=P0.11 and our custom board uses TX=P0.17 and RX=P0.18. 
 Coincidentally, my code is still monitoring the buttons on the DK board, and because of this, and although the UART is not working on my custom board, while debugging it I was seeing logs for bsp_event_t BSP_EVENT_KEY_0, which is actually pin P0.17 (the pin my board uses for UART RX), so my guess is that UART activity on my custom board is being interpreted as a button event. 
 So, the next step was to disable the call to bsp_init(), in the hopes I would be disabling button monitoring, but that is still not enough to make the UART work. 
 Question: what are the steps to allow using custom pins for UART on the nrf51822, under SDK12.3? 
 
 Best regards, 
 Ricardo

Jørgen Holmefjord · Accepted Answer

I tested your code in the UART example in SDK 12.3.0:

Fullscreen main.c Download

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/** @file
 * @defgroup uart_example_main main.c
 * @{
 * @ingroup uart_example
 * @brief UART Example Application main file.
 *
 * This file contains the source code for a sample application using UART.
 *
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include "app_uart.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "nrf.h"
#include "bsp.h"

//#define ENABLE_LOOPBACK_TEST  /**< if defined, then this example will be a loopback test, which means that TX should be connected to RX to get data loopback. */

#define MAX_TEST_DATA_BYTES     (15U)                /**< max number of test bytes to be used for tx and rx. */
#define UART_TX_BUF_SIZE 256                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE 256                         /**< UART RX buffer size. */

void uart_error_handle(app_uart_evt_t * p_event)
{
    if (p_event->evt_type == APP_UART_COMMUNICATION_ERROR)
    {
        APP_ERROR_HANDLER(p_event->data.error_communication);
    }
    else if (p_event->evt_type == APP_UART_FIFO_ERROR)
    {
        APP_ERROR_HANDLER(p_event->data.error_code);
    }
}


void uart_init(void)
{
    uint32_t err_code;

    const app_uart_comm_params_t comm_params = {
        //RX_PIN_NUMBER, TX_PIN_NUMBER,
        18,17,
        RTS_PIN_NUMBER, CTS_PIN_NUMBER,
        APP_UART_FLOW_CONTROL_DISABLED,
        false,
        UART_BAUDRATE_BAUDRATE_Baud9600
    };

    APP_UART_FIFO_INIT(&comm_params, UART_RX_BUF_SIZE, UART_TX_BUF_SIZE,
                       uart_error_handle, APP_IRQ_PRIORITY_LOWEST, err_code);
    APP_ERROR_CHECK(err_code);
}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    bsp_board_leds_init();

    uart_init();

    printf("\r\nStart: \r\n");

    while (true)
    {
        uint8_t cr;
        while (app_uart_get(&cr) != NRF_SUCCESS);
        while (app_uart_put(cr) != NRF_SUCCESS);

        if (cr == 'q' || cr == 'Q')
        {
            printf(" \r\nExit!\r\n");

            while (true)
            {
                // Do nothing.
            }
        }
    }
}


/** @} */

I tested this on a nRF51 DK by connecting P0.17 to P0.09 and P0.18 to P0.11. It seems to work fine. Can you test this on your board?

Using custom RX/TX UART pins on nrf51822

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