modbus server/slave on RS485

[ajay dange]

Hello, i am developing a modbus RTU slave on Raspberry pi.I am using libmodbus 3.0.6

Code is given below

#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <errno.h>

#include <modbus.h>

//#define MODBUS_TIMEOUT_SEC          3

//#define MODBUS_TIMEOUT_USEC         0

#define SERVER_ID                     1

#define UART_PORT                     "/dev/ttyAMA0"

#define BAUD_RATE                     19200

#define PARITY                        'N'

#define BYTESIZE                      8

#define STOPBITS                      1 

int main(void)

{

    struct timeval response_timeout;

    modbus_t *ctx;

    modbus_mapping_t *mb_mapping;

 int i;

  ctx = modbus_new_rtu(UART_PORT, BAUD_RATE, PARITY, BYTESIZE, STOPBITS);

 if (ctx == NULL) {

fprintf(stderr, "Unable to allocate libmodbus context\n");

return -1;

}

        

    /* Save original timeout */

 

response_timeout.tv_sec = MODBUS_TIMEOUT_SEC  ;

response_timeout.tv_usec = MODBUS_TIMEOUT_USEC  ;

modbus_set_response_timeout(ctx, &response_timeout);

modbus_set_debug(ctx, TRUE);

 modbus_set_slave(ctx, SERVER_ID);

 if (modbus_connect(ctx) == -1) {

fprintf(stderr, "Connexion failed: %s\n",modbus_strerror(errno));

modbus_free(ctx);

exit(-1);

}

mb_mapping = modbus_mapping_new(5, 5, 5, 5);

 if (mb_mapping == NULL) {

fprintf(stderr, "Failed to allocate the mapping: %s\n",

   modbus_strerror(errno));

modbus_free(ctx);

return -1;

}

for (;;) {

uint8_t query[MODBUS_TCP_MAX_ADU_LENGTH];

int rc;

   rc = modbus_receive(ctx, query);

if (rc != -1) {

/* rc is the query size */

modbus_reply(ctx, query, rc, mb_mapping);

} else {

/* Connection closed by the client or error */

break;

}

}

printf("Quit the loop: %s\n", modbus_strerror(errno));

modbus_mapping_free(mb_mapping);

modbus_close(ctx);

modbus_free(ctx);

return 0;

}

I have used RS 485 for this connection & connected it with my raspberry pi.

When i run this code i get following error:

ERROR Connection timed out :select

<FF><00>Quit the loop:connection timed out

please help me to resolve this issue.

-regards