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5 - Modbus

5.1 Modbus protocol

  • Modbus TCP is used for communication over LAN - functions FC: 1, 2, 3, 4, 5, 6, 15, 16
  • Modbus RTU is used for communication over RS485 - functions FC: 3, 6, 16

The states of the digital inputs must be read in full bytes from the registers of the Railduino module

5.2 Loxone Modbus TCP settings

Insert new Modbus server and set IP and port in the Modbus server settings

Create new Modbus device - and set/leave the address "1" of the Modbus client (Railduino module)
This is NOT the physical address of the device!

5.3 Loxone Modbus RTU settings


Insert new Modbus device and set the baudrate, stop bits and parity of the device (Railduino module)

5.3 Modbus register map

Modbus register map (1 register = 1 byte = 8 bits)

 0: relay outputs 1-8  
 1: relay outputs 9-12  
 2: digital outputs HSS 1-4, LSS 1-4  
 3: HSS PWM value 1 (0-255)  
 4: HSS PWM value 2 (0-255)  
 5: HSS PWM value 3 (0-255)  
 6: HSS PWM value 4 (0-255)  
 7: LSS PWM value 1 (0-255)  
 8: LSS PWM value 2 (0-255)  
 9: LSS PWM value 3 (0-255)  
 10: LSS PWM value 4 (0-255)  
 11: analog output 1  
 12: analog output 2  
 13: digital inputs 1-8  
 14: digital inputs 9-16  
 15: digital inputs 17-24  
 16: analog input 1 0-1023  
 17: analog input 2 0-1023  
 18: reset (bit 0)  
 19: 1st DS2438 Temp (value multiplied by 100)  
 20: 1st DS2438 Vad (value multiplied by 100)  
 21: 1st DS2438 Vsens (value multiplied by 100)  
 -  
 46: DS2438 values (up to 10 sensors)  
 47-57: DS18B20 Temperature (up to 10 sensors) (value multiplied by 100)