FieldServer FS-8700-73 - Manual (Page 31)

FS-8700-73 BACnet MSTP Driver Manual Page 31 of 48
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Appendix A.10. Update Property Function
The Update_Property parameter may be configured on a BACnet Server Map Descriptor in order to allow a
property other than the Present_Value to be updated in addition to the Present_Value when the Data Array value
changes.
Warning: this is a highly specialized function only to be used under very particular circumstances, by users with a
detailed understanding of BACnet and of what is to be achieved.
Appendix A.10.1. Supported values:
Present_Value (default operation)
Relinquish_Default
Appendix A.10.2. Mode of Operation when used for the Relinquish_Default property:
When the FieldServer starts up, the standard BACnet operation for AO, AV, BO and BV objects is that the
Present_Value of the object is set to the configured Relinquish_Default value. This may not be desirable in
Gateway situations where the BACnet communications module (i.e. the FieldServer) may restart independently of
the controller with the physical outputs.
Instead, it is possible to use the Update_Property setting to initialize the Relinquish_Default property using the
actual field Present_Value read from the Client Side device, so that a restart achieves two important outcomes:
The Client side outputs are not modified
The current state of the Client Side output can be read via the Relinquish_Default property. This is especially
useful since the BACnet specification makes no provision for Feedback_Values on analog objects
Depending on the function of the Client Side Map Descriptor there are slightly differing behaviors.
RDBC - If the Client Side Map Descriptor is configured with the RDBC function, then every read operation will
cause the Relinquish_Default property on the BACnet Server side to be updated to match the new
Present_Value.
ARS (recommended) - If the Client Side Map Descriptor is configured with the ARS function, then only the
startup read operation (which occurs on FieldServer restart, or if the Client Side Node has gone offline and
is being recovered) will cause theRelinquish_Default property on the BACnet Server side to be updated to
match the new Present_Value.
Restrictions:
This function cannot yet be used in conjunction with Complex data types.
Appendix A.11. Disabling selected BACnet services