Binary Input

A Binary Input object models a two-state input, such as a contact, a switch or a status signal. Its value is ACTIVE or INACTIVE. A Polarity setting lets the object invert the raw signal so the logical state is correct.

Typical uses

• A fan run status contact
• A door position switch
• A filter differential pressure switch
• A pump proof-of-flow signal

Key properties

Property	What it holds
Present_Value	The current state, ACTIVE or INACTIVE.
Polarity	Says whether the physical signal is normal or reversed relative to the logical state.
Active_Text	A label for the active state, such as ‘Running’. Inactive_Text is the other label.
Alarm_Value	The state that counts as an alarm.
Elapsed_Active_Time	How long the input has been active in total, for runtime tracking.

How it behaves

Present_Value is not commandable. The standard pairs the type with the CHANGE_OF_STATE algorithm for intrinsic reporting, using Alarm_Value. Subscribers receive a change-of-value notification whenever the state changes.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_BINARY_INPUT build option and add each object with BACnetStack_AddObject. Present_Value is enumerated, so the stack reads it through the callback you register with BACnetStack_RegisterCallbackGetPropertyEnumerated. Arm alarms with BACnetStack_SetIntrinsicChangeOfStateAlgorithmBool (an alarm value of true means active) after BACnetStack_SetAlarmsAndEventsForObjectEnabled.

Related object types

Binary Output, Binary Value, Multi-state Input

Properties

The properties ASHRAE 135-2024 clause 12.6 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	BACnetBinaryPV	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
Polarity	BACnetPolarity	R	yes	no	0
Inactive_Text	CharacterString	O2	no	no	""
Active_Text	CharacterString	O2	no	no	""
Change_Of_State_Time	BACnetDateTime	O3	no	no	No default: the read fails.
Change_Of_State_Count	Unsigned	O3	no	no	0
Time_Of_State_Count_Reset	BACnetDateTime	O3	no	no	No default: the read fails.
Elapsed_Active_Time	Unsigned32	O4	no	no	0
Time_Of_Active_Time_Reset	BACnetDateTime	O4	no	no	No default: the read fails.
Time_Delay	Unsigned	O5,7	no	no	0
Notification_Class	Unsigned	O5,7	no	no	0
Alarm_Value	BACnetBinaryPV	O5,7	no	no	0
Event_Enable	BACnetEventTransitionBits	O5,7	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O5,7	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O5,7	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O5,7	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O7	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O7	no	no	""
Event_Detection_Enable	Boolean	O5,7	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O7	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O7,8	no	no	false
Time_Delay_Normal	Unsigned	O7	no	no	0
Reliability_Evaluation_Inhibit	Boolean	O9	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Interface_Value	BACnetOptionalBinaryPV	O	no	no	Null
Audit_Level	BACnetAuditLevel	O10	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O10	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	""