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FS-8704-02_BacnetEthernet.doc Driver Manual Page 15 of 20
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Appendix A. Advanced Topics
Appendix A.1. BACnet Object Names
When an external BACnet Client builds a list of Object Names, the BACnet Server Map
Descriptor name determines the BACnet Object Name. If the Map Descriptor length is
greater than 1, then the Object Name will be suffixed with the index into the Map Descriptor.
For example, if the Map Descriptor name is SMD_AI_01 and the length 3, then the Object
Names will be SMD_AI_01[0], SMD_AI_01[1] and SMD_AI_01[2].
Appendix A.2. FieldServer implementation of BACnet priority Arrays
When writing to a BACnet Output Object, a write priority value must be specified. When the
FieldServer receives the write value, it will be stored to the Map Descriptor Priority Array
Table at the specified priority. The Priority Array Table is then scanned and the value with
the highest priority is stored to the Data Array location specified by the Map Descriptor.
When a Write “Relinquished” command is received, the value is removed from the Priority
Array Table and the next highest value from the Priority Array Table is stored to the Data
Array.
If all values have been “Relinquished” from the Priority Array Table, then the Map
Descriptors “Relinquish Default” value will be stored to the Data Array.
Appendix A.3. Accessing Priority Array information from other protocol
drivers
The Priority Array table and its “In_Use” (or Not Relinquished) state are stored internally to
every Map Descriptor, and cannot be accessed directly. If the following data arrays are
specified, however, they will maintain an exact copy of the Priority Array Table for the Map
Descriptor. Thus the Priority Array Table can be accessed.
Section Title
Map_Descriptors
Column Title Function Legal Values
DA_Pri_Array
Name of Data Array where the Priority Array
Table will be stored. Location 0 is the
Relinquish Default value and locations 1 to 16
the different entries of the Priority Array Table.
Up to 16
alphanumeric
characters
DA_Pri_Array_Offset Starting location in Data Array. 1-65535 (17)
DA_Pri_In_Use
Name of Data Array that indicates if a
particular Priority Values is in use. Location 0
indicate if the Relinquish Default has been set
and locations 1 to 16 indicate if the index is in
use (1), or if it has been Relinquished (0).
Up to 16
alphanumeric
characters
DA_Pri_In_Use_Offset Starting location in Data Array. 1-65535 (17)