ArduinoModbus : Modbus Server class
Perform a "Read Coils" operation for the specified address for a single coil.
int coilRead(int address);
int coilRead(int id, int address);
id (slave) - id of target, defaults to 0x00 if not specified
address - address to use for operation
coil value on success, -1 on failure.
ModbusServer class