int modbus_set_slave(modbus_t *ctx, int slave);
The modbus_set_slave() function shall set the slave number in the libmodbus context.
The behavior depends of network and the role of the device:
Define the slave ID of the remote device to talk in master mode or set the internal slave ID in slave mode. According to the protocol, a Modbus device must only accept message holing its slave number or the special broadcast number.
The slave number is only required in TCP if the message must reach a device on a serial network. The special value MODBUS_TCP_SLAVE (0xFF) can be used in TCP mode to restore the default value.
The broadcast address is MODBUS_BROADCAST_ADDRESS. This special value must be use when you want all Modbus devices of the network receive the request.
The modbus_set_slave() function shall return 0 if successful. Otherwise it shall return -1 and set errno to one of the values defined below.
The slave number is invalid.
The libmodbus documentation was written by StГ©phane Raimbault <email@example.com>