Nrf51822 with Modbus(TTL to RS485)

[Nidhi]

I am trying to send and receive a response from a machine using  Modbus (TTL to Rs485) and nrf51822.

Connections: R0 -> RX(P0.11) ,D1->TX(p0.09), RE&DE->P0.19,VCC->5V 

Just the same as to connect with Arduino (Have implemented with Arduino mega)

I am using Keil for programming and trying to send and receive in hexadecimal format, but I am not sure if even command is transmitted and obviously I am not getting any response.

I am not sure about connections also. Attaching code.

Please let me know where I am wrong.

#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);
    }
}
static uint8_t data_array[6];
void uart_event_handle(app_uart_evt_t * p_event)
{
   
    static uint8_t index = 0;
    uint32_t       err_code;

    switch (p_event->evt_type)
    {
        case APP_UART_DATA_READY:
            UNUSED_VARIABLE(app_uart_get(&data_array[index]));
            index++;

            if ((data_array[index - 1] == '\n') || (index > 4))
            {
               // err_code = ble_nus_string_send(&m_nus, data_array, index);
//                if (err_code != NRF_ERROR_INVALID_STATE)
//                {
//                    APP_ERROR_CHECK(err_code);
//                }

                index = 0;
							nrf_gpio_pin_set(21);
							nrf_delay_ms(100);
							nrf_gpio_pin_clear(21);
            }
            break;

        case APP_UART_COMMUNICATION_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_communication);
            break;

        case APP_UART_FIFO_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_code);
            break;

        default:
            break;
    }
}

/**
 * @brief Function for main application entry.
 */
 uint8_t check_status[5] = {0x41,0x8E,0x7E,0x7F,0x6A};
int main(void)
{
    uint32_t err_code;

    bsp_board_leds_init();

    const app_uart_comm_params_t comm_params =
      {
          RX_PIN_NUMBER,
          TX_PIN_NUMBER,
          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_event_handle,
                         APP_IRQ_PRIORITY_LOWEST,
                         err_code);

    APP_ERROR_CHECK(err_code);

//#ifndef ENABLE_LOOPBACK_TEST
    printf("\r\nStart: \r\n");
			nrf_gpio_cfg_output(19);
			nrf_gpio_cfg_output(21);
			    

     while(true)
	   {

			 nrf_gpio_pin_set(19);
		   nrf_delay_ms(55);
			for(int i=0; i<5;i++)
			{
				app_uart_put(check_status[i]);
			}
			nrf_delay_ms(2);
			nrf_gpio_pin_clear(19);
			nrf_delay_ms(3000);
	   }
       
  }

[Simonr]

I took another look at your code, and noticed that #ifndef ENABLE_LOOPBACK_TEST is commented out in your main loop. What exactly is happening with your loopback test? Also, I noticed you say RE&DE->P0.19. What are RE and DE? 

Any luck using a logic analyzer to see what's going on on the UART lines? Also, what are you supplying the Modbus with? If this is 5V as well, there might be a voltage mismatch that occurs and causes this to happen.

Best regards,

Simon

[Nidhi]

There was a voltage mismatch. The code is working. I commented on ENABLE_LOOPBACK_TEST because I don't need it. Also, RE&DE pins are enable pins for  Modbus (TTL to RS485).