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UDMI / Docs / Specs / BACnet

THIS IS A PROVISIONAL SPEC THAT IS SUBJECT TO CHANGE.

BACnet Specification

UDMI supports reading BACnet points by specifying them via a bacnet:// URL schema.

URI Schema

bacnet://<device_id>/<object_type>:<object_instance>[#property_identifier]

• device_id: The BACnet Device Object Instance Number. It uniquely identifies the BACnet device on the network.
  • Must be a positive integer in the range 1 to 4194303 (22-bit Device Object Instance range).
  • Leading zeroes are invalid (e.g., 01293 is invalid), and 0 is invalid.
• object_type: A 2 to 4 character uppercase string representing the BACnet object type (e.g., AI, AO, AV, BI, BO, BV, MSI, MSO, MSV, DO).
• object_instance: A non-negative integer representing the BACnet object instance index (e.g., 0, 1, 21, 100).
  • Leading zeroes are not allowed unless the index is 0.
• property_identifier: (Optional) A lowercase string with underscores representing the property identifier of the BACnet object, preceded by # (e.g., #present_value, #something_else).
  • If omitted, it typically defaults to the present_value property.

Object Types

The following are common BACnet object types used as part of the point reference:

• AI: Analog Input
• AO: Analog Output
• AV: Analog Value
• BI: Binary Input
• BO: Binary Output
• BV: Binary Value
• MSI: Multi-state Input
• MSO: Multi-state Output
• MSV: Multi-state Value
• DO: Device Object / Binary Output

Network Parameters

Under the localnet configuration, BACnet parameters define the communication settings:

• addr: The BACnet Device Object Instance Number. Must be a positive integer in the range 1 to 4194303 with no leading zeroes.
• network: (Optional) The 16-bit BACnet Network Number. Must be a positive integer in the range 1 to 65534 with no leading zeroes.

Examples

The metadata values in the examples below map to the following complete BACnet URIs:

• Room Temperature Sensor: bacnet://291842/AI:2#present_value
• Fan Run Status: bacnet://3/DO:0
• Discharge Air Temp: bacnet://1/AI:2
• Damper Command: bacnet://291842/BO:21

Network Configuration Example

The BACnet network specification as part of a gateway metadata.json file under localnet.families:

{
  "localnet": {
    "families": {
      "bacnet": {
        "addr": "19233",
        "network": "9288"
      }
    }
  }
}

Or defined under localnet.networks as a named BACnet network:

{
  "localnet": {
    "networks": {
      "bacnet_1": {
        "family": "bacnet",
        "addr": "19233",
        "network": "9288"
      }
    }
  }
}

Proxy Device Example

For a proxied BACnet device, the gateway block in the metadata.json specifies the protocol family, while the pointset block defines individual points and their object mappings.

{
  "gateway": {
    "target": {
      "family": "bacnet"
    }
  },
  "localnet": {
    "families": {
      "bacnet": {
        "addr": "582312"
      }
    }
  },
  "pointset": {
    "points": {
      "filter_alarm_pressure_status": {
        "units": "No-units",
        "ref": "BV:11#present_value"
      },
      "filter_differential_pressure_sensor": {
        "units": "Degrees-Celsius",
        "ref": "AV:12#present_value"
      }
    }
  }
}

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