modbus_send_raw_request(3) Manual Page

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

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.

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.

modbus_receive_confirmation(3)

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