What the Time Value Object Is
The Time Value object, defined in Clause 12.42 of ANSI/ASHRAE 135-2024, exposes a named time-of-day value inside a BACnet device to other devices on the network. It represents a single moment in the day: a start time, a setback time, a cutoff time, or any time the control logic holds and may share. It represents one specific time; the Time Pattern Value instead holds a time with wildcard fields that match many recurring times.
A Time Value can be read-only or commandable. When it is commandable, it carries the same 16-slot priority array as an Analog Output; when it is a simple stored value, it does not. Time Value objects may optionally support intrinsic reporting for fault conditions only: they perform the first stage of reliability-evaluation, apply no standardized fault or event algorithm, and deliver notifications through the event notification services.
Where You’ll See It
- Schedule anchors. An occupancy start, a setback, or a cutoff time other devices read with ReadProperty.
- Timing parameters. A daily reference time the control logic exposes.
- Configurable times. A target time an operator writes to the device.
Required Properties
Clause 12.42 requires every Time Value object to provide these properties. Datatypes are the spec’s names: Time is a time of day, CharacterString a text string, and the BACnet-prefixed types are structured values defined by the standard.
| Property | Datatype | What it holds |
|---|---|---|
Object_Identifier | BACnetObjectIdentifier | The object’s type and instance number, unique within the device |
Object_Name | CharacterString | The human-readable point name, unique within the device |
Object_Type | BACnetObjectType | Always time-value for this object |
Present_Value | Time | The time-of-day value. Read-only or commandable depending on the instance |
Status_Flags | BACnetStatusFlags | Four health flags: in-alarm, fault, overridden, out-of-service |
Property_List | BACnetARRAY[N] of BACnetPropertyIdentifier | The list of properties this instance actually implements |
When the object is commandable, it additionally implements Priority_Array (the 16 command slots), Relinquish_Default (the fallback when all slots are Null), and Current_Command_Priority. On a simple stored Time Value these are absent. See How Commanding Works on the Analog Output page for the priority-array model.
Optional Properties
The properties integrators meet most are Description, the command-tracking group on commandable instances, and Reliability, which names the reason whenever the fault flag in Status_Flags is set. The intrinsic-reporting group generally appears or is absent as a set and, on this object, drives fault reporting only.
| Property | Datatype | Group |
|---|---|---|
Description | CharacterString | General |
Out_Of_Service | BOOLEAN | General |
Event_State | BACnetEventState | General |
Priority_Array | BACnetPriorityArray | Commanding |
Relinquish_Default | Time | Commanding |
Current_Command_Priority | BACnetOptionalUnsigned | Commanding |
Value_Source | BACnetValueSource | Commanding |
Value_Source_Array | BACnetARRAY[16] of BACnetValueSource | Commanding |
Last_Command_Time | BACnetTimeStamp | Commanding |
Command_Time_Array | BACnetARRAY[16] of BACnetTimeStamp | Commanding |
Time_Delay | Unsigned | Intrinsic reporting |
Notification_Class | Unsigned | Intrinsic reporting |
Event_Enable | BACnetEventTransitionBits | Intrinsic reporting |
Acked_Transitions | BACnetEventTransitionBits | Intrinsic reporting |
Notify_Type | BACnetNotifyType | Intrinsic reporting |
Event_Time_Stamps | BACnetARRAY[3] of BACnetTimeStamp | Intrinsic reporting |
Event_Message_Texts | BACnetARRAY[3] of CharacterString | Intrinsic reporting |
Event_Message_Texts_Config | BACnetARRAY[3] of CharacterString | Intrinsic reporting |
Event_Detection_Enable | BOOLEAN | Intrinsic reporting |
Reliability | BACnetReliability | Fault detection |
Reliability_Evaluation_Inhibit | BOOLEAN | Fault detection |
Audit_Level | BACnetAuditLevel | Auditing |
Auditable_Operations | BACnetAuditOperationFlags | Auditing |
Tags | BACnetARRAY[N] of BACnetNameValue | Tagging and profile |
Profile_Location | CharacterString | Tagging and profile |
Profile_Name | CharacterString | Tagging and profile |
Related Objects
- Time Pattern Value: holds a time with wildcard fields that match many recurring times, unlike this single-time object.
- Date Value: the equivalent for a calendar date.
- DateTime Value: the equivalent for a combined date and time.
What Chipkin Provides
The Time Value object, in both read-only and commandable forms, is a first-class object type in the CAS BACnet Stack. Talk to us about modeling your device’s points.