The Modbus master function includes the following two:
- 1-to-1 Modbus/VRF gateway with Modbus master function (usually customized product by gateway suppliers)
- 1-to-n Modbus/VRF gateway with Modbus master function or an additional Modbus master unit
The Modbus master manages communication between VRF HMI units (slave function) and the Modbus gateway to ensure proper operation. When using a Modbus gateway without Modbus master function, an additional Modbus master unit is required.
RDF280.V.. does not have termination resistor.
For VRF systems with multiple indoor units
If its VRF outdoor unit (2-pipe system) can only support either heating or cooling control sequence each time, only Modbus master or VRF HMI units selected as Master unit can select the fixed heating or cooling control sequence for the VRF system.
- When heating mode is selected, the Modbus master also sets P01 of each connected VRF HMI slave unit = 4 (HEAT/FAN) only.
- When cooling mode is selected, the Modbus master also sets P01 of each connected VRF HMI slave unit = 5 (COOL/FAN/Dehumidification) or 6 (COOL/FAN) depending on VRF operating modes supported by the indoor units.
If, e.g., heating is selected, RDF280.V.. can only select VRF operating modes: HEAT or FAN. If cooling is selected, RDF280.V.. can only select VRF operating mode: COOL, FAN or Dehumidification.
If a VRF outdoor unit (4-pipe system) allows both heating and cooling control sequences selected by individual indoor units, each connected VRF HMI unit can be preset with P01 = 0, 1, 2 or 3 according to the VRF operating modes supported by the indoor and outdoor units. Note that some indoor units do not support AUTO or Dehumidification.