Multi-state Value

A Multi-state Value object holds one numbered state that the device keeps for its own purposes, such as an operating mode or a status code. It is not tied to a physical input or output. The object reports how many states exist and can label each one.

Typical uses

• Building mode: Occupied, Unoccupied, Standby
• Setpoint profile selector
• Equipment status code with named states
• Season selector: Heating, Cooling, Auto
• Alarm priority level

Key properties

Property	What it holds
Present_Value	The current state, a number from 1 to Number_Of_States.
Number_Of_States	How many states the value can take.
State_Text	An optional array of labels, one per state.
Alarm_Values	The states that count as an alarm, when the object reports intrinsic events.
Priority_Array	Optional. Present only when the value is made commandable; sixteen slots, one per priority.
Relinquish_Default	Optional. The state used when every priority slot is empty.

How it behaves

Without a priority array, a client can write the value only if the device allows it; with one, the value is commandable. When it reports intrinsic events, the standard pairs it with the CHANGE_OF_STATE algorithm: the object goes off-normal when Present_Value enters one of the Alarm_Values and returns to normal when it leaves them. 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_MULTISTATE_VALUE build option and add each object with BACnetStack_AddObject. Serve Present_Value with the callback you register with BACnetStack_RegisterCallbackGetPropertyUnsignedInteger and, if clients may write it, the BACnetStack_RegisterCallbackSetPropertyUnsignedInteger callback. The object becomes commandable once you enable both PriorityArray and RelinquishDefault; from then on the stack reads the priority array through the callbacks instead of the plain getter. To arm alarms, enable alarms for the object and call BACnetStack_SetIntrinsicChangeOfStateAlgorithmUnsigned once for each alarm state. Call BACnetStack_UpdateValue whenever the value you serve changes, so COV, trend logs and alarms see it.

Related object types

Multi-state Input, Multi-state Output, Integer Value

Properties

The properties ASHRAE 135-2024 clause 12.20 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.
Present_Value	Unsigned	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.
Description	CharacterString	O	no	no	""
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	R	yes	no	0
Reliability	BACnetReliability	O	no	no (yes while Out_Of_Service is true)	0
Out_Of_Service	Boolean	R	yes	no	false
Number_Of_States	Unsigned	R	yes	no	No default: value-not-initialized until a callback or a client write supplies one.
State_Text	BACnetARRAY[N] of CharacterString	O	no	no	""
Priority_Array	BACnetARRAY[16] of BACnetOptionalUnsigned	O3	no	no	Built by the stack from your callbacks.
Relinquish_Default	Unsigned	O3	no	no	No default: value-not-initialized until a callback or a client write supplies one.
Time_Delay	Unsigned	O4,6	no	no	0
Notification_Class	Unsigned	O4,6	no	no	0
Alarm_Values	BACnetLIST of Unsigned	O4,6	no	no	0
Fault_Values	BACnetLIST of Unsigned	O8	no	no	0
Event_Enable	BACnetEventTransitionBits	O4,6	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O4,6	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O4,6	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O4,6	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_Detection_Enable	Boolean	O4,6	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O6	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O6,7	no	no	false
Time_Delay_Normal	Unsigned	O6	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O8	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Current_Command_Priority	BACnetOptionalUnsigned	O3	no	no	Built by the stack from your callbacks.
Value_Source	BACnetValueSource	O9,11,13	no	no	No default: the read fails.
Value_Source_Array	BACnetARRAY[16] of BACnetValueSource	O10,12	no	no	No default: the read fails.
Last_Command_Time	BACnetTimeStamp	O10,12	no	no	No default: the read fails.
Command_Time_Array	BACnetARRAY[16] of BACnetTimeStamp	O12	no	no	No default: the read fails.
Audit_Level	BACnetAuditLevel	O14	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O14	not in profile	not in profile	No default: the read fails.
Audit_Priority_Filter	BACnetOptionalPriorityFilter	O15	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	""