Simple UART program doesn't send data to another device

[davidm]

Hi all,

I am trying to send data from nrf52840 to Arduino. I have a simple UART program running on nrf52840 that is supposed to transmit a character to another device(Arduino in this case) through TX/RX. I just want it to send a character 'a' for now.I have tested the program with CoolTerm , and it works fine but whenever I connect to another device ,nothing is received in another device.I am suspecting it might be GPIO issue, I am currently using the default RX_PIN_NUMBER 8, TX_PIN_NUMBER 6.I have tried to change Rx Tx to 26 and 27 respectively but no luck. What I am doing wrong? Below is the slightly modified  Uart program

int main(void) {
    ...
    while (true)
    {
       while (app_uart_put('a') != NRF_SUCCESS);
       
       while (app_uart_get(&cr) != NRF_SUCCESS);
       if (cr=='q'    || cr=='Q'){
            printf("\r\nExit \r\n");
            while(true){
               // Do nothing
            }
       }
	}
}

[Susheel Nuguru]

You need to first initialize app_uart module to be able to use it.

Please look at the example in SDK15.3\examples\peripheral\uart\main.c

[davidm]

Yes I initiliazed it, I am using the same code in\examples\peripheral\uart\main.c  .Keep in mind I mentioned that it works when I send to CoolTerm terminal.

[Susheel Nuguru]

The code snippet you showed was confused me as you showed the whole main function without uart initialization. Can you give me your project so that I do a quick test? 

[davidm]

Ok Thank you , here is full code, I am currently using SDK 15.2, but i tried 15.3 was the same outcome

#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"
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"
#if defined (UART_PRESENT)
#include "nrf_uart.h"
#endif
#if defined (UARTE_PRESENT)
#include "nrf_uarte.h"
#endif


//#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);
    }
}


#ifdef ENABLE_LOOPBACK_TEST
/* Use flow control in loopback test. */
#define UART_HWFC APP_UART_FLOW_CONTROL_ENABLED

/** @brief Function for setting the @ref ERROR_PIN high, and then enter an infinite loop.
 */
static void show_error(void)
{

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


/** @brief Function for testing UART loop back.
 *  @details Transmitts one character at a time to check if the data received from the loopback is same as the transmitted data.
 *  @note  @ref TX_PIN_NUMBER must be connected to @ref RX_PIN_NUMBER)
 */
static void uart_loopback_test()
{
    uint8_t * tx_data = (uint8_t *)("\r\nLOOPBACK_TEST\r\n");
    uint8_t   rx_data;

    // Start sending one byte and see if you get the same
    for (uint32_t i = 0; i < MAX_TEST_DATA_BYTES; i++)
    {
        uint32_t err_code;
        while (app_uart_put(tx_data[i]) != NRF_SUCCESS);

        nrf_delay_ms(10);
        err_code = app_uart_get(&rx_data);

        if ((rx_data != tx_data[i]) || (err_code != NRF_SUCCESS))
        {
            show_error();
        }
    }
    return;
}
#else
/* When UART is used for communication with the host do not use flow control.*/
#define UART_HWFC APP_UART_FLOW_CONTROL_DISABLED
#endif


/**
 * @brief Function for main application entry.
 */
int main(void)
{    
    uint32_t err_code;

    bsp_board_init(BSP_INIT_LEDS);

    const app_uart_comm_params_t comm_params =
      {
          RX_PIN_NUMBER,
          TX_PIN_NUMBER,
          RTS_PIN_NUMBER,
          CTS_PIN_NUMBER,
          UART_HWFC,
          false,
#if defined (UART_PRESENT)
          NRF_UART_BAUDRATE_115200
#else
          NRF_UARTE_BAUDRATE_115200
#endif
      };

    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);

#ifndef ENABLE_LOOPBACK_TEST
    printf("\r\nUART example started2.\r\n");
 
    while (true)
    { 
        while (app_uart_put('7') != NRF_SUCCESS);
    }
#else

    // This part of the example is just for testing the loopback .
    while (true)
    {
        uart_loopback_test();
    }
#endif
}


/** @} */

[Susheel Nuguru]

tried your code on putty/TeraTerm and connected it to another device in receive mode. All of them work as they should. Something must be wrong with how you have configured the RX pin on the peer device.

[davidm]

Thank you for trying. what is the other device you used, I tried with Arduino and esp32 but both didn't work.And the Pin I used are RX-08 and TX-06 on NRF52840.