What the DateTime Value Object Is
The DateTime Value object, defined in Clause 12.38 of ANSI/ASHRAE 135-2024, exposes a named combined date-and-time value inside a BACnet device to other devices on the network. It pairs a calendar date with a time of day to represent a single moment: a last-run timestamp, a next-event time, or any date-and-time the control logic holds and may share. It represents one specific moment; the DateTime Pattern Value instead holds date and time fields with wildcards that match many recurring moments.
A DateTime 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. DateTime 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
- Timestamps. A last-run, last-service, or next-scheduled moment other devices read with ReadProperty.
- Event markers. A stored moment the control logic exposes for coordination.
- Configurable date-times. A target moment an operator writes to the device.
Required Properties
Clause 12.38 requires every DateTime Value object to provide these properties. Datatypes are the spec’s names: BACnetDateTime pairs a calendar date and a time of day, CharacterString is 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 datetime-value for this object |
Present_Value | BACnetDateTime | The combined date-and-time 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 DateTime 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, Is_UTC (whether the value is expressed in UTC), and, on commandable instances, the command-tracking group. 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 |
Is_UTC | BOOLEAN | General |
Priority_Array | BACnetPriorityArray | Commanding |
Relinquish_Default | BACnetDateTime | 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
- DateTime Pattern Value: holds date and time fields with wildcards that match many recurring moments, unlike this single-moment object.
- Date Value: the equivalent for a calendar date alone.
- Time Value: the equivalent for a time of day alone.
What Chipkin Provides
The DateTime 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.