Time Value

A Time Value object holds one time of day under a name. Use it to publish a time that is not the clock itself, such as an opening hour, a start time or the time of the last event. Clients read it and, if the device allows, write it.

Typical uses

• Building opening time
• Daily start time for a pump
• Time of the last alarm
• Cutoff time for a daily report
• Setting an operator can change

Key properties

Property	What it holds
Present_Value	The time of day the object holds, down to hundredths of a second.
Priority_Array	Optional. Present only when the value is commandable; sixteen priority slots.
Relinquish_Default	Optional. The time used when every priority slot is empty.
Out_Of_Service	When true, Present_Value stops following its source and a client can write it for testing.

How it behaves

The object is not commandable unless you give it a priority array. The standard applies no event algorithm to it, so it reports faults only. COV notifications go out on any change to Present_Value or Status_Flags.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_TIME_VALUE build option and add each object with BACnetStack_AddObject. Serve Present_Value with the callback you register with BACnetStack_RegisterCallbackGetPropertyTime and, if clients may write it, the BACnetStack_RegisterCallbackSetPropertyTime callback. 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. Call BACnetStack_UpdateValue whenever the value you serve changes, so COV, trend logs and alarms see it.

Related object types

Time Pattern Value, Date Value, DateTime Value

Properties

The properties ASHRAE 135-2024 clause 12.42 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	Time	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 BACnetOptionalTime	O2	no	no	Built by the stack from your callbacks.
Relinquish_Default	Time	O2	no	no	No default: value-not-initialized until a callback or a client write supplies one.
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	""