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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, const 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. The public header of libmodbus provides a list of supported Modbus functions codes, prefixed by MODBUS_FC_ (eg. MODBUS_FC_READ_HOLDING_REGISTERS), to help build of raw requests. RETURN VALUE The 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, MODBUS_FC_READ_HOLDING_REGISTERS, 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 StA(C)phane Raimbault <stephane.raimbault@gmail.com> libmodbus v3.1.6 08/10/2020 MODBUS_SEND_RAW_REQU(3)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | SEE ALSO | AUTHORS
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