Multi-state Output

A Multi-state Output object models an output that can take one of several numbered states, such as a fan with Off, Low, Medium and High. A client writes the state number to command it. The object reports the number of states and can carry a text label for each one.

Typical uses

• Fan speed selection: Off, Low, Medium, High
• Chiller or boiler operating mode
• Damper or valve preset position
• Lighting scene selector
• Pump staging mode

Key properties

Property	What it holds
Present_Value	The commanded state, a number from 1 to Number_Of_States. A client writes it at a priority; the value in force is the highest-priority entry of the priority array.
Number_Of_States	How many states the output has. Valid values of Present_Value run from 1 up to this number.
State_Text	An optional array of labels, one per state. Clients show these instead of bare numbers.
Priority_Array	Sixteen slots, one per command priority. A slot is either empty (relinquished) or holds a state.
Relinquish_Default	The state used when every slot of the priority array is empty.
Feedback_Value	Optional. The state the physical equipment reports back, used to detect a command that did not take effect.

How it behaves

The object is always commandable. When it reports intrinsic events, the standard pairs it with the COMMAND_FAILURE algorithm: the object goes off-normal when the commanded state and Feedback_Value disagree for the time delay, and returns to normal once they agree again. 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_OUTPUT build option and add each object with BACnetStack_AddObject. The stack always treats this type as commandable. It reads the priority array, one slot at a time, through the callback you register with BACnetStack_RegisterCallbackGetPropertyBool (is the slot empty) and the BACnetStack_RegisterCallbackGetPropertyUnsignedInteger callback (the state), and applies writes through the BACnetStack_RegisterCallbackSetPropertyUnsignedInteger callback. It never calls the plain Present_Value getter. To alarm on a disagreement with the feedback, enable alarms for the object and call BACnetStack_SetIntrinsicCommandFailureAlgorithm. 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 Value, Binary Output

Properties

The properties ASHRAE 135-2024 clause 12.19 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	W	yes	yes	Built by the stack from the priority array your callbacks serve, or Relinquish_Default when every slot is empty.
Description	CharacterString	O	no	no	""
Device_Type	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	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	R	yes	no	Built by the stack from your callbacks.
Relinquish_Default	Unsigned	R	yes	no	No default: value-not-initialized until a callback or a client write supplies one.
Time_Delay	Unsigned	O1,3	no	no	0
Notification_Class	Unsigned	O1,3	no	no	0
Feedback_Value	Unsigned	O1	no	no	0
Event_Enable	BACnetEventTransitionBits	O1,3	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O1,3	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O1,3	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O1,3	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O3	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O3	no	no	""
Event_Detection_Enable	Boolean	O1,3	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O3	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O3,4	no	no	false
Time_Delay_Normal	Unsigned	O3	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O5	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Interface_Value	BACnetOptionalUnsigned	O	no	no	Null
Current_Command_Priority	BACnetOptionalUnsigned	R	yes	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	""