Siemens SIMATIC PN/BACnet LINK, Руководство по эксплуатации

Страница: 37 / 96

Functions
4.4 Data exchange between PN/BACnet LINK and other BACnet devices
PN/BACnet LINK
Operating Instructions, 10/2017, A5E39895543-AA
37
Reading values
For read values, you can determine whether they are read cyclically or if a registration for a
message is to take place in case of value change (COV).
If "Registration for value change" is activated in the configuration, the following procedure
applies:
The PN/BACnet LINK checks whether the device supports COV. If the device does not
support COV, it is read cyclically automatically. Cyclic reading uses the time set by the user
for the update cycle.
If the device supports COV, the PN/BACnet LINK attempts to register for the time interval
configured by the user. Once the time interval elapses, the PN/BACnet LINK attempts to
register itself again.
If the registration attempt fails, the system automatically reads cyclically.
Causes for a failure of the registration can be, for example, a configured time interval for new
registration that is not supported or too many COV subscriptions.
4.4.2 Data transfer as server
Transmission types
Possible transmission types:
● Direct write or read accesses from other BACnet devices
● Sending values if the value changes
Sending values
The maximum lifetime accepted by the PN/BACnet LINK for incoming registration requests is
8 hours. All registration requests with a longer lifetime are rejected by PN/BACnet LINK.
The maximum number of COV subscriptions is 1000. The PN/BACnet LINK rejects any
additional registration requests.