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1 FUNCTIONS
1.4 BACnet Request Function (Read Function)
Operation of a BACnet module
Operation at startup
A BACnet module initializes an access block for reading with '0' at the startup of the module.
Cyclic operation
• When '1' (send request) is stored to the CONTROL in a BACnet module, the instance number of a destination device,
ObjectIdentifier, PropertyIdentifier, and ArrayIndex of an access block for reading are read. Then, a ReadPropertyMultiple
service, which reads property values, is sent, and '2' (sending) is stored to the CONTROL.
• If invalid information is stored to the instance number of the destination device, ObjectIdentifier, PropertyIdentifier, or
ArrayIndex, '7' (invalid information) will be stored to the STATUS, and '4' (error end) will be stored to the CONTROL.
• After a reply (ComplexAck) to the ReadPropertyMultiple service is received from a read target device, the read data is
stored to the access block for reading, and '3' (normal completion) is stored to the CONTROL.
• If an error response (Error, Reject, or Abort) or the excess of the maximum number of retries (Retry limit exceeded) is
received from the read target device, '7' (invalid information) will be stored to the STATUS, and '4' (error end) will be stored
to the CONTROL.
However, when a Reject (unrecognized-service) is received, the ReadPropertyMultiple service is changed to a
ReadProperty service, and the service is sent again.
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