CharacterString Value

A CharacterString Value holds a piece of text as its Present_Value. A device uses it to publish a status message, a name or a mode that is better as text than as a number.

Typical uses

• A current operating mode as text
• The last fault message
• A firmware or site label
• A product name read by supervisors

Key properties

Property	What it holds
Present_Value	The text. Clients read it and, where the host allows, write it.
Alarm_Values	With intrinsic reporting, the strings that put the object into OFFNORMAL.
Priority_Array	Present only when the object is commandable.
Relinquish_Default	Present only when the object is commandable. Used when no priority slot holds a value.

How it behaves

With intrinsic reporting, the standard pairs a CharacterString Value with the CHANGE_OF_CHARACTERSTRING algorithm. The object goes OFFNORMAL when Present_Value contains one of the alarm strings, case-sensitively, for the time delay. Clients can subscribe to changes of Present_Value and Status_Flags.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_CHARACTER_STRING_VALUE build option and add each object with BACnetStack_AddObject. Present_Value is served through the callback you register with BACnetStack_RegisterCallbackGetPropertyCharacterString and the BACnetStack_RegisterCallbackSetPropertyCharacterString callback. The object becomes commandable once you enable both PriorityArray and RelinquishDefault. Arm the alarm with BACnetStack_SetIntrinsicChangeOfCharacterstringAlgorithm, which takes a list of alarm strings and their character sets. Call BACnetStack_SetAlarmsAndEventsForObjectEnabled first.

Related object types

OctetString Value, BitString Value, Integer Value, Multi-state Value

Properties

The properties ASHRAE 135-2024 clause 12.37 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	CharacterString	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	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 BACnetOptionalCharacterString	O2	no	no	Built by the stack from your callbacks.
Relinquish_Default	CharacterString	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 BACnetOptionalCharacterString	O3,5	no	no	No default: the read fails.
Fault_Values	BACnetARRAY[N] of BACnetOptionalCharacterString	O7	no	no	No default: the read fails.
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	O9,11	no	no	No default: the read fails.
Command_Time_Array	BACnetARRAY[16] of BACnetTimeStamp	O11	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	""