NAME

       modbus_send_raw_request - send a raw request

SYNOPSIS

       int modbus_send_raw_request(modbus_t *ctx, uint8_t *raw_req, int 'raw_req_length);

DESCRIPTION

       The modbus_send_raw_request() function shall send a request via the socket of the context
       ctx. This function must be used for debugging purposes because you have to take care to
       make a valid request by hand. The function only adds to the message, the header or CRC of
       the selected backend, so raw_req must start and contain at least a slave/unit identifier
       and a function code. This function can be used to send request not handled by the library.

RETURN VALUE

       The modbus_send_raw_request() function shall return the full message length, counting the
       extra data relating to the backend, if successful. Otherwise it shall return -1 and set
       errno.

EXAMPLE

           modbus_t *ctx;
           /* Read 5 holding registers from address 1 */
           uint8_t raw_req[] = { 0xFF, 0x03, 0x00, 0x01, 0x0, 0x05 };
           int req_length;
           uint8_t rsp[MODBUS_TCP_MAX_ADU_LENGTH];

           ctx = modbus_new_tcp("127.0.0.1", 1502);
           if (modbus_connect(ctx) == -1) {
               fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
               modbus_free(ctx);
               return -1;
           }

           req_length = modbus_send_raw_request(ctx, raw_req, 6 * sizeof(uint8_t));
           modbus_receive_confirmation(ctx, rsp);

           modbus_close(ctx);
           modbus_free(ctx);

SEE ALSO

       modbus_receive_confirmation(3)

AUTHORS

       The libmodbus documentation was written by Stéphane Raimbault
       <stephane.raimbault@gmail.com[1]>

NOTES

        1. stephane.raimbault@gmail.com
           mailto:stephane.raimbault@gmail.com