MODBUS_SEND_RAW_REQU(3) Libmodbus Manual MODBUS_SEND_RAW_REQU(3)
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
", 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 Stephane Raimbault <stephane.raimbault@gmail.com[1]>
NOTES
1. stephane.raimbault@gmail.com
mailto:stephane.raimbault@gmail.com
libmodbus 3.0.3 05/26/2012 MODBUS_SEND_RAW_REQU(3)