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
