DateTime Value

A DateTime Value holds one date and time as its Present_Value. A device uses it to publish a moment that is not tied to hardware, such as when a process last ran or when a fault began.

Typical uses

• The time of the last backup
• When a fault started
• The next planned shutdown
• The last time a filter was changed

Key properties

Property	What it holds
Present_Value	The date and time. Clients read it and, where the host allows, write it.
Is_UTC	Says whether the value is in UTC or in local time.
Priority_Array	Present only when the object is commandable.
Relinquish_Default	Present only when the object is commandable. Used when no priority slot holds a value.

How it behaves

The standard defines no event algorithm for this type. With intrinsic reporting it reports faults only. Clients can subscribe to changes of Present_Value and Status_Flags.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_DATE_TIME_VALUE build option and add each object with BACnetStack_AddObject. Present_Value is served through the callback you register with BACnetStack_RegisterCallbackGetPropertyDate and the BACnetStack_RegisterCallbackGetPropertyTime callback together. The object becomes commandable once you enable both PriorityArray and RelinquishDefault. The standard applies no event algorithm to this type and the stack serves no event state for it, so there is nothing to arm: BACnetStack_SetAlarmsAndEventsForObjectEnabled accepts the object but changes nothing a client can see.

Related object types

Date Value, Time Value, DateTime Pattern Value, Schedule

Properties

The properties ASHRAE 135-2024 clause 12.38 defines for this object type.

How to read the table:

• Conformance is what the standard asks of every object of this type: R is required, W is required and writable by a client, O is optional. A digit after the letter marks a condition in the standard that decides when the property is present or writable, such as support for intrinsic reporting.
• Present by default: yes means the stack presents the property as soon as you add the object; no means it is optional and you turn it on with BACnetStack_SetPropertyEnabled. This is the stack’s starting setup, so it can differ from the conformance code.
• Writable is whether a client can write the property by default. Change it with BACnetStack_SetPropertyWritable.
• not in profile means the stack does not offer this property for this object type.
• Value when your callback does not answer: “Held by the stack” means the stack stores and serves the value itself and does not ask your callbacks. Otherwise it is the value the stack answers when your callback declines or is not registered.

Property	Datatype	Conformance	Present by default	Writable	Value when your callback does not answer
Object_Identifier	BACnetObjectIdentifier	R	yes	no	Held by the stack.
Object_Name	CharacterString	R	yes	no	"Object <type>,<instance>", such as "Object 0,1" for Analog Input 1.
Object_Type	BACnetObjectType	R	yes	no	Held by the stack.
Description	CharacterString	O	no	no	""
Present_Value	BACnetDateTime	R1	yes	no (yes while Out_Of_Service is true)	No default: value-not-initialized. Once Priority_Array and Relinquish_Default are enabled, built by the stack from the priority array your callbacks serve.
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	O	no	no	0
Reliability	BACnetReliability	O	no	no (yes while Out_Of_Service is true)	0
Out_Of_Service	Boolean	O	no	no	false
Priority_Array	BACnetARRAY[16] of BACnetOptionalDateTime	O2	no	no	Built by the stack from your callbacks.
Relinquish_Default	BACnetDateTime	O2	no	no	No default: value-not-initialized until a callback or a client write supplies one.
Is_UTC	Boolean	O	no	no	false
Reliability_Evaluation_Inhibit	Boolean	O3	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Event_Detection_Enable	Boolean	O4,5	no	no	false
Notification_Class	Unsigned	O4,5	no	no	0
Event_Enable	BACnetEventTransitionBits	O4,5	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O4,5	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O4,5	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O4,5	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O5	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O5	no	no	""
Current_Command_Priority	BACnetOptionalUnsigned	O2	no	no	Built by the stack from your callbacks.
Value_Source	BACnetValueSource	O6,8,10	no	no	No default: the read fails.
Value_Source_Array	BACnetARRAY[16] of BACnetValueSource	O7,9	no	no	No default: the read fails.
Last_Command_Time	BACnetTimeStamp	O7,9	no	no	No default: the read fails.
Command_Time_Array	BACnetARRAY[16] of BACnetTimeStamp	O9	no	no	No default: the read fails.
Audit_Level	BACnetAuditLevel	O11	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O11	not in profile	not in profile	No default: the read fails.
Audit_Priority_Filter	BACnetOptionalPriorityFilter	O11	not in profile	not in profile	No default: the read fails.
Tags	BACnetARRAY[N] of BACnetNameValue	O	no	no	No default: the read fails.
Profile_Location	CharacterString	O	no	no	""
Profile_Name	CharacterString	O	no	no	""