Vijeo Designer uses ModbusRTU or Modbus/TCP to read and write data to a M171/172 HVAC controller. Only Machine Expert HVAC - SoMachine HVAC Status Variables have an assigned modbus address. Therefore only Status Variables can be Viewed and written to by a Magelis HMI. You can define Status Variables in you SoMachine HVAC project in the Resources Tab. When you create a Status Variable, Machine Expert HVAC - SoMachine HVAC automatically assigns an address to the variable. Such as 8960. In Vijeo Designer you would reference that address by using 48960 in your variable definition window.