Multi-state Input

A Multi-state Input object reports one of a fixed number of named states from a sensor or process, as a number starting at 1. Use it where a reading has more than two meaningful values, such as a fan speed or an operating mode.

Typical uses

• Report a fan as off, low, medium or high
• Show an HVAC unit’s operating mode
• Report the position of a rotary selector switch
• Expose a chiller sequence step

Key properties

Property	What it holds
Present_Value	The current state, a whole number from 1 up to Number_Of_States.
Number_Of_States	How many states the input can have.
State_Text	A text label for each state, shown to operators. Optional.
Alarm_Values	The states that raise an alarm. Optional.
Fault_Values	The states that mean the input is faulty. Optional.

How it behaves

A Multi-state Input is read-only unless Out_Of_Service is true, when a client can write Present_Value for testing. Where it reports events itself, the standard pairs it with the CHANGE_OF_STATE algorithm: it goes off-normal when Present_Value matches an alarm value and returns to normal when it leaves them. The FAULT_STATE fault algorithm can set Reliability. It sends change-of-value notices when Present_Value changes.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_MULTISTATE_INPUT build option and add each object with BACnetStack_AddObject. Serve Present_Value with the callback you register with BACnetStack_RegisterCallbackGetPropertyUnsignedInteger; Object_Name uses the BACnetStack_RegisterCallbackGetPropertyCharacterString callback. It is not commandable. Arm state alarms with BACnetStack_SetAlarmsAndEventsForObjectEnabled and then BACnetStack_SetIntrinsicChangeOfStateAlgorithmUnsigned.

Related object types

Multi-state Output, Multi-state Value, Binary Input

Properties

The properties ASHRAE 135-2024 clause 12.18 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.
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 (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	""
Time_Delay	Unsigned	O3,5	no	no	0
Notification_Class	Unsigned	O3,5	no	no	0
Alarm_Values	BACnetLIST of Unsigned	O3,5	no	no	0
Fault_Values	BACnetLIST of Unsigned	O7	no	no	0
Event_Enable	BACnetEventTransitionBits	O3,5	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O3,5	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O3,5	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O3,5	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	""
Event_Detection_Enable	Boolean	O3,5	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O5	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O5,6	no	no	false
Time_Delay_Normal	Unsigned	O5	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O7	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Interface_Value	BACnetOptionalUnsigned	O	no	no	Null
Audit_Level	BACnetAuditLevel	O8	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O8	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	""