Global Group

A Global Group object collects property values from many objects, in this device or elsewhere on the network, and presents them as one list. A client reads one object instead of polling every point. It can also watch the status flags of its members and raise an alarm.

Typical uses

• Read all floor temperatures in one request
• Send a snapshot of many points when an alarm occurs
• Group points from several devices for a dashboard
• Alarm when any monitored point goes into alarm or fault

Key properties

Property	What it holds
Group_Members	The list of objects and properties that belong to the group. Members may be in other devices.
Group_Member_Names	A name for each member, in the same order as Group_Members.
Present_Value	The current values of all members, read in one go.
Member_Status_Flags	A summary of the members’ status flags. The alarm algorithm watches it.
Requested_Update_Interval	How often, in hundredths of a second, the group should refresh its values. Update_Interval reports the rate actually achieved.

How it behaves

A Global Group is not commandable. The standard pairs it with the CHANGE_OF_STATUS_FLAGS algorithm, and with the FAULT_STATUS_FLAGS fault algorithm for Reliability. It can also send periodic change-of-value notices through its COV properties.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_GLOBAL_GROUP build option and add each object with BACnetStack_AddObject; serve Object_Name with the callback you register with BACnetStack_RegisterCallbackGetPropertyCharacterString. Arm the status-flags alarm with BACnetStack_SetAlarmsAndEventsForObjectEnabled and then BACnetStack_SetIntrinsicChangeOfStatusFlagsAlgorithm, and the fault side with BACnetStack_SetFaultStatusFlagsAlgorithm.

Related object types

Group, Structured View, Notification Class

Properties

The properties ASHRAE 135-2024 clause 12.50 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	""
Group_Members	BACnetARRAY[N] of BACnetDeviceObjectPropertyReference	R	yes	no	No default: the read fails.
Group_Member_Names	BACnetARRAY[N] of CharacterString	O	no	no	""
Present_Value	BACnetARRAY[N] of BACnetPropertyAccessResult	R	yes	no	No default: value-not-initialized.
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	R	yes	no	0
Member_Status_Flags	BACnetStatusFlags	R	yes	no	An empty bit string.
Reliability	BACnetReliability	O	no	no	0
Out_of_Service	Boolean	R	yes	no	false
Update_Interval	Unsigned	O	no	no	0
Requested_Update_Interval	Unsigned	O	no	no	0
COV_Resubscription_Interval	Unsigned	O	no	no	0
Client_COV_Increment	BACnetClientCOV	O	no	no	No default: the read fails.
Time_Delay	Unsigned	O1,4	no	no	0
Notification_Class	Unsigned	O1,4	no	no	0
Event_Enable	BACnetEventTransitionBits	O1,4	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O1,4	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O1,4	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O1,4	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O4	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O4	no	no	""
Event_Detection_Enable	Boolean	O1,4	no	no	false
Event_Algorithm_Inhibit_Ref	BACnetObjectPropertyReference	O4	no	no	No default: the read fails.
Event_Algorithm_Inhibit	Boolean	O4,5	no	no	false
Time_Delay_Normal	Unsigned	O4	no	no	0
COVU_Period	Unsigned	O2	no	yes	0
COVU_Recipients	BACnetLIST of BACnetRecipient	O2	no	yes	No default: the read fails.
Reliability_Evaluation_Inhibit	Boolean	O6	no	no	false
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Audit_Level	BACnetAuditLevel	O7	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O7	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	""