BitString Value

A BitString Value holds a string of bits as its Present_Value. It suits a set of related flags that a device wants to publish as one value, such as a status word. Each bit can have its own meaning, described in Bit_Text.

Typical uses

• A status word from a drive
• A set of fault flags from a controller
• A bit mask of enabled features
• A bank of digital input states read as one value

Key properties

Property	What it holds
Present_Value	The bit string. Clients read all the bits at once.
Bit_Text	Optional array of labels, one per bit, so a client can show what each bit means.
Bit_Mask	With intrinsic reporting, selects which bits are watched for alarms.
Alarm_Values	With intrinsic reporting, the bit patterns that put the object into OFFNORMAL.

How it behaves

With intrinsic reporting, the standard pairs a BitString Value with the CHANGE_OF_BITSTRING algorithm. The object goes OFFNORMAL when the watched bits match an alarm value for the time delay.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_BITSTRING_VALUE build option and add each object with BACnetStack_AddObject. Present_Value is served through the callback you register with BACnetStack_RegisterCallbackGetPropertyBitString and the BACnetStack_RegisterCallbackSetPropertyBitString callback. The object becomes commandable once you enable both PriorityArray and RelinquishDefault. Arm the alarm with BACnetStack_SetIntrinsicChangeOfBitstringAlgorithm, which reaches the first 32 bits, or BACnetStack_SetIntrinsicChangeOfBitstringAlgorithm64, which reaches up to 64. Each takes one alarm value. Call BACnetStack_SetAlarmsAndEventsForObjectEnabled first.

Related object types

OctetString Value, Integer Value, Binary Value, CharacterString Value

Properties

The properties ASHRAE 135-2024 clause 12.40 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	BitString	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.
Bit_Text	BACnetARRAY[N] of CharacterString	O	no	no	""
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	O3	no	no	0
Reliability	BACnetReliability	O	no	no (yes while Out_Of_Service is true)	0
Out_Of_Service	Boolean	O	no	no	false
Priority_Array	BACnetARRAY[16] of BACnetOptionalBitString	O2	no	no	Built by the stack from your callbacks.
Relinquish_Default	BitString	O2	no	no	No default: value-not-initialized until a callback or a client write supplies one.
Time_Delay	Unsigned	O3,5	no	no	0
Notification_Class	Unsigned	O3,5	no	no	0
Alarm_Values	BACnetARRAY[N] of BitString	O3,5	no	no	An empty bit string.
Bit_Mask	BitString	O3,5	no	no	An empty bit string.
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.
Current_Command_Priority	BACnetOptionalUnsigned	O2	no	no	Built by the stack from your callbacks.
Value_Source	BACnetValueSource	O8,10,12	no	no	No default: the read fails.
Value_Source_Array	BACnetARRAY[16] of BACnetValueSource	O9,11	no	no	No default: the read fails.
Last_Command_Time	BACnetTimeStamp	O	no	no	No default: the read fails.
Command_Time_Array	BACnetARRAY[16] of BACnetTimeStamp	O	no	no	No default: the read fails.
Audit_Level	BACnetAuditLevel	O13	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O13	not in profile	not in profile	No default: the read fails.
Audit_Priority_Filter	BACnetOptionalPriorityFilter	O13	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	""