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Read-only or Read/Write status of AVs in Room Controller device created in MPM


When a Room Controller device is created under an MPM using one of the predefined devices in Building Expert, a number of its BACnet objects are mapped to AVs in the MPM. It is not possible to tell from the AV properties if the BACnet objects are read-only or read/write.

Product Line

EcoStruxure Building Expert


  • MPM
  • SmartStruxure Lite


When a Room Controller device is added under an MPM using one of the predefined devices in Building Expert, a number of its BACnet objects are mapped to AVs in the MPM.  The BACnet objects made visible to the MPM are a small subset of the total number of BACnet objects in the device and consist of several different BACnet types, some of which are read-only and others are read/write.  Regardless of the BACnet type, they are all mapped to AVs whose properties do not distinguish between read-only and read/write objects.


There is little documentation available on the predefined devices found in Building Expert. The best source of information is in PIC Statements and BACnet - Integration Guides.

As an example I will use the SE8600UxB room controller. The "SE8600 Series BACnet - Integration Guide" is available on Exchange Download Center.

In the MPM we have created a Lua script which monitors the occupancy status of the SE8600 and under certain conditions sets it to UnOccupied then turns it off after a delay. For this to work we need to know which AVs we can monitor and write to. Among the AVs mapped to the MPM for this device are "Occupancy Command", "Effective Occupancy" and "System Mode", which would seem to be suitable.

The "SE8600 Series BACnet - Integration Guide" lists hundreds of BACnet properties of various object types, only 12 of which are mapped to the MPM. These 12 properties all appear as AVs in the MPM, regardless of their original BACnet object type. Also, although the object tables in the document list the read/write status of most of the objects, they do not list it for the objects mapped to the MPM.

The only way to find out is to scan through the various tables of objects until you find one whose name matches one of the AVs in our example. Make a note of which table it is in.

In our example:
"Occupancy Command" and "System Mode" are in the MV table
"Effective Occupancy" is in the MI table

On page 35, under "Summary for Integrators", there is this line: "AI’s, BI’s & MI’s are not writable and are typically only used for status".
"Effective Occupancy" appears in the MI object table, so it is read-only.
As "Occupancy Command" and "System Mode" are in the MV table they are read/write.

This procedure is applicable to all the Room Controllers available via the "Add Devices" command in Building Expert.

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