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8.1 Trend Process Description
Startup Sequence
1) Power up
2) Waiting for initial scan
3) Perform initial HVAC scan
4) Initial scan complete
5) Connect to CNC port
6) Transfer current HVAC status to required Trend outstation (“First Pass”)
7) Disconnect from CNC port
8) Wait for re-connection time
9) Connect to CNC port
10) Poll the objects for each active HVAC unit in the Trend outstation, then either
Update the HVAC if the value of a Trend object has been altered, or
Update the Trend object if the value of an HVAC parameter has changed.
11) Disconnect from CNC port
12) Wait for re-connection time
13) Goto 9
At power-up, the Black Pear will wait for the initial HVAC scan to begin. During this scan,
all available ‘active’ HVAC units are discovered. Once the scan is complete, the Black
Pear will transfer all current parameter settings to the appropriate objects in the destination
Trend outstation. This process is called the ‘First Pass’. This ensures that the values in the
Black Pear and the Trend device are in sync. Until the ‘First Pass’ is complete, all
commands sent from the Trend network to the Black Pear will be ignored.
The re-connection time is calculated from the CNC Usage setting within the Black Pear.
This ensures that all Black Pear devices sharing a single CNC have enough time to
connect.
Notes:
Some Trend systems will generate ‘network alarms’ due to the repeated connection
and disconnection of the Black Pear to the CNC.
Setting the CNC Usage = 0 will allow a single Black Pear to remain connected to the CNC,
thus preventing these alarms from being generated.
This feature was added in firmware v2.19.
Following a reconfiguration of the Trend outstation, it is important
that the Black Pear is restarted, to guarantee that all parameters are
in sync.
