Command prioritization
Command prioritization provides a mechanism to determine which process or user role has precedence over lower prioritized processes or user-roles. BACnet specifies 16 levels of priorities, where 1 is specified as the highest (Manual Life-Safety) Priority where 16 specifies the lowest and default priority.
The Present_Value is always taken from the value in the highest prioritized slot. A client may remove a priority at a specific slot by writing a value of NULL at the given priority.
If no priority is active (all 16 slots having a value NULL), the value for the Present_Value property is taken from the Relinquish_Default property.
The priority is specified using a WriteProperty or WritePropertyMultiple service. If the priority is missing, 16 will be used as the default priority.
Priority | Meaning |
|---|---|
1 | Manual Life-Safety |
2 | Automatic Life-Safety |
3 | Available |
4 | Available |
5 | Critical Equipment Control, e. g. defrost |
6 | Minimum On-/Off |
7 | Available |
8 | Manual Operator, e. g. BMS |
9 | Available |
10 | Available |
11 | Available |
12 | Available |
13 | Available |
14 | Available |
15 | Available |
16 | Available (Default, if no priority is specified) |
Function blocks with the suffix “_5P” implement a total of 5 of the 16 possible priorities (which is normally enough for most projects).