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FS-8704-06 BACnet IP Driver Manual
Appendix B. Advanced Topics
Appendix B.1.
When an external BACnet Client builds a list of Object Names, the BACnet Server Map Descriptor
names determine the BACnet Object Name. If the Map Descriptor length is greater than 1, 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 B.2.
FieldServer implementation of BACnet priority Arrays
When BACnet Output objects are written to the Server side of the FieldServer, an associated write
priority is given to each write value. When the FieldServer receives the write value, it stores it 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.
Accessing Priority Array information
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
DA_Pri_Array
DA_Pri_Array_Offset*
DA_Pri_In_Use
DA_Pri_In_Use_Offset*
Appendix B.3.
The BACnet PTP client driver can read multiple BACnet objects using the Read_Property_Multiple
service under the following conditions:
The number of objects to be read must not exceed 29.
•
No gaps must exist in the range of object to be read.
•
The Map Descriptor function must be of the Read type. (e.g. Rdbc)
•
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BACnet object names
BACnet Priority Arrays
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.
Starting location in Data Array.
Name of Data Array that indicates if a particular
Priority Value is in use. Location 0 indicates whether
the Relinquish Default has been set and locations 1
to 16 indicate whether the index is in use (1), or
Relinquished (0).
Starting location in Data Array.
Limitations of the BACnet Read_Property_Multiple service.
Function
Page 14 of 24
Legal Values
Up to 16
alphanumeric
characters
1-65535 ,0
Up to 16
alphanumeric
characters
1-65535, 0
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