When you click with a component highlighted in the Bacnet Export Manager, the Add dialog (Figure 83) contains a number of fields with either default or empty values, described below.
All fields in this dialog apply separately to each highlighted (for export) component, as follows:
Select Type first, before editing other fields such as Object Name and Description. Otherwise, those entries become cleared and you will need
to re-enter.In addition, Type is the only slot you cannot change after adding (say, in the Edit dialog).
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Name
Niagara read-only component name for the Bacnet export descriptor, which defaults to the combination of
<object type>_<instance number>. Reflects the “Type” chosen (below it in dialog). -
Object Name
The “exposed to BACnet” name for this object. By default, the entire component path under the station’s Config is included, using period (“.”) delimiters between
parent.childlevels. This enforces (externally) the BACnet requirement for unique names for all objects in a device.You can shorten or edit object name, either now or later. However, please note that each Object Name should be unique among
all server descriptors under the Export Table. The Batch Search and Replace feature 
is useful when adding/editing multiple exports.
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Type
Initially (in Add dialog) you can select the specific Bacnet export descriptor (object type)—in most cases, from two or more choices. Click the drop down control (Figure 84) to select type.
Writable Niagara components typically offer more type selections than read-only points, such as:
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Two read-only: “input” or “value” type, e.g. Binary Input or Binary Value object.
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Two writable: “output” or “prioritized value” type, e.g. Binary Output or Binary Value Prioritized object.
Figure 85 shows an example of type selections when exporting an NdioBooleanWritable point.
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Object Type
Reflects the “BACnet Object type” exposed, dependent on Type selection.
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Inst Num
The instance number portion of this object’s “Object ID,” which must be unique within the station for this (exported) BACnet Object type. By default, the export manager enforces this.
If you are exporting a group of points at once, you can select them all in the Add/Edit dialog, and type the instance number
for the first one, and each descriptor will be assigned successive instance numbers as available.
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Export Ord
Station’s Ord location of the source component. By default, format used is the numeric “handle” instead of slot (better if source object gets renamed). In an Edit (dialog) scenario, you can access a more meaningful ord by clicking the right-side Folder control. This produces a popup Select Ord dialog, showing the component’s location in the station’s component tree hierarchy.
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Description
Optional text string; this appears as the Description property value in the exposed BACnet object.
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BACnet Writable
(“Dimmed” if the export Type is read-only, for example Analog Input or Binary Value)
For writable types, an array of checkboxes lets you select the specific priority levels externally exposed to BACnet to accept writes. Included are “all controls” to clear or select, see Figure 86. (For “full BACnet compliance,” all levels must be selected—however, see the Note below).
Each priority level (1—16) that you enable for BACnet writes results in that “InN” input on the source component to be linked to this “Bacnet export descriptor” component. These links appear as “nubs” when viewing the source writable point in its wire sheet view.Do not select any priority level already linked or in use by Niagara, otherwise control contention will occur. Also see Allowing write access from BACnet.
After creation (adding) Bacnet export descriptors, note that each descriptor also has additional properties accessible in its property sheet, along with those seen in the Add and Edit dialog. See the next section, Properties of Bacnet export descriptors for more details.