Group

A Group object bundles a list of objects and properties inside one device. A client reads the group’s Present_Value to get all those values in one response. It saves many separate reads when a screen or report needs the same set of points each time.

Typical uses

• Read all zone temperatures on a floor in one request
• Collect the key readings of a boiler plant
• Give a workstation one object per dashboard page
• Combine setpoints and status from related points

Key properties

Property	What it holds
List_Of_Group_Members	The members. Each is an object plus the properties of it to include. A client can change the list in devices that allow it.
Present_Value	A list with one result per member holding the current values of the chosen properties. Read-only.

How it behaves

A Group object is read-only and has no alarm or change-of-value behaviour of its own. A client reads Present_Value and gets the current values of every member. A member that cannot be read shows an error inside its own result, and the rest still return. Members must be in the same device.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_GROUP build option. Create the object with BACnetStack_AddObject first, then call BACnetStack_AddGroupObject. Add members with BACnetStack_AddGroupMember; call it again with the same member and a different property to give that member more properties. Remove a member with BACnetStack_RemoveGroupMember. The stack stores List_Of_Group_Members, builds Present_Value from it by itself and also handles AddListElement and RemoveListElement. Serve Object_Name with the callback you register with BACnetStack_RegisterCallbackGetPropertyCharacterString, and Description if you enable it with BACnetStack_SetPropertyEnabled.

Related object types

Global Group, Structured View, Channel

Properties

The properties ASHRAE 135-2024 clause 12.14 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	""
List_Of_Group_Members	BACnetLIST of ReadAccessSpecification	R	yes	no	Held by the stack.
Present_Value	BACnetLIST of ReadAccessResult	R	yes	no	Built by the stack from List_Of_Group_Members.
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Audit_Level	BACnetAuditLevel	O1	not in profile	not in profile	No default: the read fails.
Auditable_Operations	BACnetAuditOperationFlags	O1	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	""