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7 BACnet Communication
3-102
WindO/I-NV4 User’s Manual
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Unsubscribed COV (COVU) function
In the COVU (Change Of Value Unsubscribed) function, the MICRO/I spontaneously provides notification that
Present_Value or Status_Flags of a specific object has changed to all BACnet devices connected to the same network.
The properties of objects that correspond to the COVU function and the timing of when to provide notification of
changes are given as follows.
The MICRO/I implements the COVU function by sending the Unconfirmed COV Notification service to BACnet devices.
For example, when BACnet/IP is started with AI-10 (Analog Input object, instant number 10) having the status in the
following table, notification is provided on the status of the properties at the set cycle (Unsubscribed COV frequency).
*1 Refer to “BACnet/IP Settings” on page 3-108.
Object Properties Timing to Provide Notification of Change
Analog Input
Analog Output
Analog Value
Present_Value
Status_Flags
Notification of the status is provided at the interval of the Unsubscribed COV frequency
*1
.
Notification of change is also provided when (1) or (2) as follows.
(1)
When Present_Value has changed to a value greater than or equal to the value set
for COV_Increment (starting point is from when the previous COV notification was
sent)
(2) When any of the bits in Status_Flags have changed
Binary Input
Binary Output
Binary Value
Present_Value
Status_Flags
Notification of change is provided when (1) or (2) as follows.
(1) When
Present_Value
has changed
(2) When any of the bits in Status_Flags have changed
AI-10 Properties Value
Present_Value 10.0
COV_Increment 3.0
Status_Flags { }
BACnet
device (2)
BACnet
device (1)
MICRO/I
Unsubscribed COV frequency
Present_Value of AI-10 is 10.0.
Status_Flags is { }.
Present_Value of AI-10: 10.0
Status_Flags: { }
Present_Value of AI-10: 15.0
Status_Flags: {FAULT}
Present_Value of AI-10 has changed to 15.
Status_Flags is {FAULT}.
COV notification transmission
Present_Value of AI-10 is 10.0.
Status_Flags is { }.
COV notification transmission
Present_Value of AI-10 is 15.0.
Status_Flags is {FAULT}.
COV notification transmission
COV notification transmission
• When using the COVU function, the values of properties can be regularly sent to BACnet devices,
regardless of any change in the value of the properties.
• The COVU function can be set for each object.
• Only one Unsubscribed COV Frequency can be set for the MICRO/I. Different frequencies cannot be set
for each object.
• If the Unsubscribed COV Frequency is set to 0, the COV function is stopped, and notification is provided
only when there is a change in the target property.
• When the Unsubscribed COV frequency is changed by a device address, the change will be applied after
the service is next initiated.
• Notification may not be provided for changes in values that are faster than the synchronization cycle of
objects and device addresses.