Documentation
The documentation is provided with libmodbus releases as man pages (generated from doc sources. You can also browse the documentation of the different releases of libmodbus:
See the Wiki for general informations.
Code Sample
#include <stdio.h>
#include <modbus.h>
int main(void) {
modbus_t *mb;
uint16_t tab_reg[32];
mb = modbus_new_tcp("127.0.0.1", 1502);
modbus_connect(mb);
/* Read 5 registers from the address 0 */
modbus_read_registers(mb, 0, 5, tab_reg);
modbus_close(mb);
modbus_free(mb);
}