code: final public void writeSingleRegister(int serverAddress, int startAddress, int register) throws
              ModbusProtocolException, ModbusNumberException, ModbusIOException {
          processRequest(ModbusRequestBuilder.getInstance().buildWriteSingleRegister(serverAddress, startAddress, register));
      }
docs: This function code is used to write a single holding register in a remote device.
  The Request PDU specifies the address of the register to be written. Registers are addressed
  starting at zero. Therefore register numbered 1 is addressed as 0.
  
  @param serverAddress a slave address
  @param startAddress  the address of the register to be written
  @param register      value
  @throws ModbusProtocolException if modbus-exception is received
  @throws ModbusNumberException   if response is invalid
  @throws ModbusIOException       if remote slave is unavailable