Event Log

An Event Log object keeps a buffer of the event notifications the device receives. Clients read the records back later. A device uses it to give operators a history of alarms that survives a missed notification.

Typical uses

• Keep the last 500 alarms on a building controller
• Let a workstation catch up on alarms it missed while offline
• Record events from several field controllers in one place
• Tell a client when enough new records exist to read

Key properties

Property	What it holds
Log_Buffer	The stored event records. Clients read it with ReadRange, not ReadProperty.
Enable	Turns logging on or off.
Buffer_Size	The most records the buffer holds.
Record_Count	How many records are in the buffer now.
Total_Record_Count	A running count of every record ever added. Clients and the BUFFER_READY algorithm use it to see how much is new.
Stop_When_Full	When true, logging stops at a full buffer. When false, the oldest records are overwritten.

How it behaves

An Event Log is not commandable. The standard pairs it with the BUFFER_READY algorithm. When Notification_Threshold more records have been added since the last notification, it sends a to-normal notification so clients know to read the new records.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_EVENT_LOG build option. Create it with BACnetStack_AddEventLogObject, giving the buffer size; do not use BACnetStack_AddObject, because reads then abort. The stack stores Enable, Stop_When_Full, the record counts, the threshold properties and the buffer itself, so callbacks cannot override them. Records come only from event notifications the device receives; there is no function to add one yourself. Serve Object_Name with the callback you register with BACnetStack_RegisterCallbackGetPropertyCharacterString. Start_Time and Stop_Time are optional; turn them on with BACnetStack_SetPropertyEnabled. Arm the buffer-ready notice with BACnetStack_SetAlarmsAndEventsForObjectEnabled and then BACnetStack_SetIntrinsicBufferReadyAlgorithm.

Related object types

Trend Log, Trend Log Multiple, Notification Class, Audit Log

Properties

The properties ASHRAE 135-2024 clause 12.27 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.
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Description	CharacterString	O	no	no	""
Status_Flags	BACnetStatusFlags	R	yes	no	Held by the stack.
Event_State	BACnetEventState	R	yes	no	NORMAL, or the alarm engine’s state once alarms are enabled.
Reliability	BACnetReliability	O	no	no	0
Enable	Boolean	W	yes	yes	Held by the stack.
Start_Time	BACnetDateTime	O1,2	no	yes	Held by the stack.
Stop_Time	BACnetDateTime	O1,2	no	yes	Held by the stack.
Stop_When_Full	Boolean	R	yes	no	Held by the stack.
Buffer_Size	Unsigned32	R	yes	no	Held by the stack.
Log_Buffer	BACnetLIST of BACnetEventLogRecord	R	yes	no	Held by the stack. Read it with ReadRange; a ReadProperty is refused.
Record_Count	Unsigned32	W	yes	yes	Held by the stack.
Total_Record_Count	Unsigned32	R	yes	no	Held by the stack.
Notification_Threshold	Unsigned32	O3,5	no	no	Held by the stack.
Records_Since_Notification	Unsigned32	O3,5	no	no	Held by the stack.
Last_Notify_Record	Unsigned32	O3,5	no	no	Held by the stack.
Notification_Class	Unsigned	O3,5	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
Reliability_Evaluation_Inhibit	Boolean	O7	no	no	false
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	""