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Communication sequence
System Initialization
At start-up, all registers have the value 0.
been completed, and that all indoor and outdoor register values have been updated.
If bit 0 of the communication status register for an indoor unit is 0, it means that this indoor unit is not connected.
After the power is turned on, the BMS periodically reads the communication status register values of indoor units. Then, if
unit from that time.
Monitor and operate units from the BMS
When the BMS writes a value to the holding register, a control command is sent to the relevant indoor unit.
The holding register value for an indoor unit is not updated until a changed status value is received from that indoor unit.
Because the user might be able to operate indoor units with a remote control, the BMS must reads their status periodically.
If communication between an indoor/outdoor unit and the Modbus interface module is stopped, the last status value is
retained until communication is resumed.
BMS
Check
communication
status.
Monitoring
&
control
Power on
Check communication status (51).
Response: 0 (Not Ready)
Check communication status (51).
Response: 7 (Ready)
Check indoor status
(input & holding registers).
Response: Status
Change a value in the holding registers.
Check indoor status
(input & holding registers).
Response: Status
Modbus
interface module
Communication status
(51 bits 0 to 2): 0 (Not Ready)
Tracking
Communication status
(51 bits 0 to 2) : 7 (Ready)
Change a value.
Response
Indoor unit
Power on
Response: Status
Response: Status
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