What B-ASC Is
A BACnet device profile is a standardized capability level: a checklist of things a device must be able to do before it can wear the label. B-ASC (BACnet Application Specific Controller) is defined in Annex L of ANSI/ASHRAE 135-2024 (clause L.4.3) as a controller with limited resources relative to a B-AAC, built for one specific application with limited programmability.
The checklist items are BACnet Interoperability Building Blocks (BIBBs), each a named unit of capability such as “can answer read requests” (DS-RP-B). B-ASC is a data-sharing device with no alarming, scheduling, or trending requirement. It serves its values, accepts writes, answers discovery, and honors communication control. A device documents its claim in its PICS (Protocol Implementation Conformance Statement); to verify a claim, ask for the PICS and check the profile line.
Where It’s Used
B-ASC is the profile for the large population of fixed-function field controllers that do their job locally and expose points to the network.
- Terminal-unit controllers. VAV boxes, fan-coil units, and heat-pump controllers running a fixed sequence, exposing sensor and setpoint points.
- Packaged equipment controllers. A factory-programmed controller on a piece of equipment that presents its points but does not originate alarms over BACnet.
- Fixed-function zone controllers. Devices with a set application where alarming and scheduling live in the supervisory tier, not the controller.
Required Services
The table below is the exhaustive service set required by the B-ASC BIBBs. Initiates means the device sends the request or notification; Executes means the device receives and acts on it (responding, for confirmed services). BIBB codes encode the same split: a -A BIBB is the initiating side, a -B BIBB the executing side. A - means the profile does not require that direction; a device may still support it.
| Capability area | Service | Required by BIBB | Initiates | Executes |
|---|---|---|---|---|
| Data sharing | ReadProperty | DS-RP-B | - | Yes |
| Data sharing | WriteProperty | DS-WP-B | - | Yes |
| Device and network management | Who-Is | DM-DDB-B | - | Yes |
| Device and network management | I-Am | DM-DDB-B | Yes | - |
| Device and network management | Who-Has | DM-DOB-B | - | Yes |
| Device and network management | I-Have | DM-DOB-B | Yes | - |
| Device and network management | DeviceCommunicationControl | DM-DCC-B | - | Yes |
A device on an MS/TP segment configured as a subordinate may be exempt from the dynamic-binding rows (DM-DDB-B, DM-DOB-B).
Related Profiles
| Profile | How it differs from B-ASC |
|---|---|
| B-AAC | Advanced Application Controller: a step up. Adds alarming, local scheduling, and ReadPropertyMultiple |
| B-SA | Smart Actuator: similar data sharing, without the communication-control requirement |
| B-SS | Smart Sensor: read-only, the minimal profile |
What Chipkin Provides
The CAS BACnet Stack implements the full BIBB set the B-ASC profile requires. Talk to us about building or integrating a B-ASC device on the stack.