OctetString Value

An OctetString Value object holds a string of raw bytes under a name. Use it for data that is not text and not a number, such as a binary key, a hardware address or a block of packed data. Clients read it, and may write it if the device allows.

Typical uses

• MAC or hardware address of an attached device
• Firmware or configuration checksum
• Opaque identifier read from a card or tag
• Packed status bytes from equipment
• Binary key or token a client may write

Key properties

Property	What it holds
Present_Value	The bytes the object holds. A client reads them as a byte string of any length the device supports.
Priority_Array	Optional. Present only when the value is commandable; sixteen priority slots.
Relinquish_Default	Optional. The value used when every priority slot is empty.
Out_Of_Service	When true, Present_Value stops following the real source and a client can write it for testing.

How it behaves

The object is not commandable unless you give it a priority array. It has no event algorithm and no intrinsic reporting. 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_OCTET_STRING_VALUE build option and add each object with BACnetStack_AddObject. Serve Present_Value with the callback you register with BACnetStack_RegisterCallbackGetPropertyOctetString and, if clients may write it, the BACnetStack_RegisterCallbackSetPropertyOctetString callback. The object becomes commandable once you enable both PriorityArray and RelinquishDefault. Alarms are not available for this type: BACnetStack_SetAlarmsAndEventsForObjectEnabled returns false for it. Call BACnetStack_UpdateValue whenever the value you serve changes, so COV, trend logs and alarms see it.

Related object types

CharacterString Value, BitString Value, Integer Value

Properties

The properties ASHRAE 135-2024 clause 12.41 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	OctetString	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.
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	O	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 BACnetOptionalOctetString	O2	no	no	Built by the stack from your callbacks.
Relinquish_Default	OctetString	O2	no	no	No default: value-not-initialized until a callback or a client write supplies one.
Reliability_Evaluation_Inhibit	Boolean	O3	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	O4,6,8	no	no	No default: the read fails.
Value_Source_Array	BACnetARRAY[16] of BACnetValueSource	O5,7	no	no	No default: the read fails.
Last_Command_Time	BACnetTimeStamp	O5,7	no	no	No default: the read fails.
Command_Time_Array	BACnetARRAY[16] of BACnetTimeStamp	O7	no	no	No default: the read fails.
Audit_Level	BACnetAuditLevel	O9	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O9	not in profile	not in profile	No default: the read fails.
Audit_Priority_Filter	BACnetOptionalPriorityFilter	O9	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	""