BACnet Device Service

The BACnet Device Services integrate the BACnet protocol with Edge Xpert.

Key Features

The BACnet Device Service acts as a BACnet client. There are two BACnet Device Services:

• BACnet/IP
• BACnet/MSTP

Both versions support the reading and writing data values on a BACnet device. For further information, refer to the official ASHRAE SSPC 135 website.

BACnet ReadPropertyMultiple and WritePropertyMultiple

The BACnet protocol traditionally has the option for reading and writing multiple properties in the same command. Previous versions of the Edge Xpert BACnet device service implemented this as a distinct option in device provisioning. This has now been incorporated into the device service and occurs automatically. This can be disabled with the DisableMultiRead and DisableMultiWrite environment variables. Additionally, the maximum number of reads and writes within a command can now be specified with the MultiReadBatch environment variable.

BACnet Discovery

The BACnet Device Service implements a discovery feature. This allows the automatic onboarding of BACnet devices discovered on the network. This reduces the complexity and allows BACnet devices to be onboarded quickly and easily.

Supported Data Types

When the device receives a request, it returns a value with a BACnet type. The following table lists the BACnet data types and their equivalent EdgeXpert data types for individual BACnet property elements:

BACnet Array types can be read but will only be returned in the Edge Xpert String type where each element is comma-separated. The following BACnet types are supported for the array:

• Boolean
• Enumerated
• Unsigned Int
• Signed Int
• Real
• Double
• Character String
• Null

BACnet Device Profile

The device profile defines what resources are available on a particular device. Ensure that the following profile attributes are defined in the device profile:

BACnet Protocol Properties

The available BACnet protocol properties are described in the following table:

BACnet Priority Levels

When performing a put request on a BACnet device resource, an additional option can be added to the URL query parameter, Priority, which indicates the priority level (1 to 16) of the value. Only a select few Object types and properties support these priority levels in BACnet.

An example is provided that demonstrates its usage on the Present Value property of the Analog Output Object. In this example, priority level 2 will be set as the value 33.0.

curl -g --request PUT 'http://<bacnet-service-address>:59882/api/v2/device/name/bacnet-ip-sim/analog_output_0-present-value?options={"Priority":2}' \
--header 'Content-Type: application/json' \
--data-raw '{
    "analog_output_0-present-value": 33.0
}'

These priority levels can also be set to null. In the following example, priority level 1 will be set to null. This will mean that when the Present Value property is read, the returned reading will skip priority level 1 as its null and return the value from level 2 which was set as 33.0.

curl -g --request PUT 'http://<bacnet-service-address>:59882/api/v2/device/name/bacnet-ip-sim/analog_output_0-present-value?options={"Priority":1}' \
--header 'Content-Type: application/json' \
--data-raw '{
    "analog_output_0-present-value": null
}'

Using the BACnet Device Service

An example of setting up and using devices with the Edge Xpert BACnet Device Service can be found at BACnet/IP Example and BACnet/MSTP Example.