ArduinoModbus : Modbus Server class
Perform a "Read Holding Registers" operation for a single holding register.
long holdingRegisterRead(int address);
long holdingRegisterRead(int id, int address);
id (slave) - id of target, defaults to 0x00 if not specified
address - start address to use for operation
holiding register value on success, -1 on failure.
ModbusServer class
