Timer

A Timer object is a countdown timer that clients can see and control. A client starts it, stops it or forces it to expire, and reads how much time remains. It can write values into other objects when it starts, expires or stops.

Typical uses

• Run a fan for 15 minutes after a button press
• Bathroom or hallway light timeout
• Hold an override for a set time, then release it
• Delay before a pump restarts
• Alarm when a timer expires

Key properties

Property	What it holds
Present_Value	Remaining time in milliseconds while the timer runs, and zero otherwise. Writing a time starts the timer.
Timer_State	Idle, running or expired. A client writes idle to clear the timer.
Timer_Running	True while the timer runs. Writing true starts it with Default_Timeout; writing false while it runs makes it expire.
Default_Timeout	The duration used when a client starts the timer by writing Timer_Running.
State_Change_Values	The value to write to the referenced properties for each kind of state change.
List_Of_Object_Property_References	The properties that receive those values.

How it behaves

The object has no priority array. When it reports intrinsic events, the standard pairs it with the CHANGE_OF_TIMER algorithm, which goes off-normal when Timer_State enters a chosen state, typically expired.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_TIMER build option. It is on in the full target; in the embedded target, define it yourself (see Configuring a build). CASBACnetStackDLL.h has no function dedicated to this type, so create it with BACnetStack_AddObject. The stack serves the object identifier, object type, property list and status flags itself; your callbacks serve every other property, so your application runs the countdown. To arm alarms, enable alarms for the object and call BACnetStack_SetIntrinsicChangeOfTimerAlgorithm, which needs both STACK_OPTION_ALARMS_AND_EVENTS and STACK_OPTION_OBJECT_TYPE_TIMER. Call BACnetStack_UpdateValue for Timer_State when it changes, or no event is ever sent.

Related object types

Schedule, Calendar, Command

Properties

The properties ASHRAE 135-2024 clause 12.57 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	Unsigned	R1	yes	no (yes while Out_Of_Service is true)	No default: value-not-initialized.
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	O3	no	no	0
Reliability	BACnetReliability	O1	no	no (yes while Out_Of_Service is true)	0
Out_Of_Service	Boolean	O	no	no	false
Timer_State	BACnetTimerState	R2	yes	no	0
Timer_Running	Boolean	R2	yes	no	false
Update_Time	BACnetDateTime	O3	no	no	No default: the read fails.
Last_State_Change	BACnetTimerTransition	O	no	no	0
Expiration_Time	BACnetDateTime	O	no	no	No default: the read fails.
Initial_Timeout	Unsigned	O	no	no	0
Default_Timeout	Unsigned	O	no	no	0
Min_Pres_Value	Unsigned	O4	no	no	0
Max_Pres_Value	Unsigned	O4	no	no	0
Resolution	Unsigned	O	no	no	0
State_Change_Values	BACnetARRAY[7] of BACnetTimerStateChangeValue	O5	no	no	No default: the read fails.
List_Of_Object_Property_References	BACnetLIST of BACnetDeviceObjectPropertyReference	O5	no	no	Held by the stack.
Priority_For_Writing	Unsigned(1..16)	O5	no	no	0
Event_Detection_Enable	Boolean	O3,6	no	no	false
Notification_Class	Unsigned	O3,6	no	no	0
Time_Delay	Unsigned	O3,6	no	no	0
Time_Delay_Normal	Unsigned	O3,6	no	no	0
Alarm_Values	BACnetLIST of BACnetTimerState	O3,6	no	no	0
Event_Enable	BACnetEventTransitionBits	O3,6	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O3,6	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O3,6	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O3,6	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O6	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O6	no	no	""
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O6	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O6,7	no	no	false
Reliability_Evaluation_Inhibit	Boolean	O8	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Audit_Level	BACnetAuditLevel	O9	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O9	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	""