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UART communication between two boards

Hi,

I am trying to establish UART communication between two nRF52 Dev boards. I flashed both of them with UART peripheral example from 15.2.0 SDK and connected TX,RX and GND pins.

Here, I encountered a weird issue where the two way communication(two terminals are recording the data when I enter data on any one terminal) is taking place with only one connection (TX from one board to RX on another / Connecting RX of both connectors) and nothing is being displayed on terminals when TX on both boards are connected. Can anyone explain this?

Thank you.

  • I'm afraid I haven't been able to reproduce this on my side.

    Maybe you could upload a picture of your setup with the nRF52-DK's?

    Also, you are using an unmodified version of the UART Hardware peripheral example?
    Located in <sdk_root>/examples/peripheral/uart

    Best regards,
    Joakim.

  • Hi Joakim,

    Sorry for the delay. This is the setup with the nRF52 DK's.

    I connected the grounds on both boards(black wire). Also connected TX on board 1 (P0.06) to RX on board 2 (P0.08) using green wire. 

    The code that I flashed on both boards is:

    /**
     * Copyright (c) 2014 - 2018, Nordic Semiconductor ASA
     *
     * All rights reserved.
     *
     * Redistribution and use in source and binary forms, with or without modification,
     * are permitted provided that the following conditions are met:
     *
     * 1. Redistributions of source code must retain the above copyright notice, this
     *    list of conditions and the following disclaimer.
     *
     * 2. Redistributions in binary form, except as embedded into a Nordic
     *    Semiconductor ASA integrated circuit in a product or a software update for
     *    such product, must reproduce the above copyright notice, this list of
     *    conditions and the following disclaimer in the documentation and/or other
     *    materials provided with the distribution.
     *
     * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
     *    contributors may be used to endorse or promote products derived from this
     *    software without specific prior written permission.
     *
     * 4. This software, with or without modification, must only be used with a
     *    Nordic Semiconductor ASA integrated circuit.
     *
     * 5. Any software provided in binary form under this license must not be reverse
     *    engineered, decompiled, modified and/or disassembled.
     *
     * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
     * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
     * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
     * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
     * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
     * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     *
     */
    /** @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"
    #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 started.\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')
            {
                while (app_uart_get(&cr) != NRF_SUCCESS);
                printf(" \r\nValue: %d\r\n", cr);
            }
        }
    #else
    
        // This part of the example is just for testing the loopback .
        while (true)
        {
            uart_loopback_test();
        }
    #endif
    }
    
    
    /** @} */
    

    After flashing, I opened putty emulator for UART ports on both boards. When I send characters from board 1; they are displayed on terminal for board 2. 

    Next, when I send characters from board 2, they are being displayed on terminal for board 1 when I didn't connect board 2 TX to board1 RX.

    What might be the reason?

    Thank you.

  • Hi again.

    Thank you for the detailed description of your setup.

    We have been able to reproduce it using the same setup as you.
    However, I must admit that I don't know why that is working.

    I will do some digging and see if I can find an explanation to this.

    Best regards.

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