Default Topics and Descriptions
Review the following information on default topics and descriptions.
Data Publishing Formats
DeviceHub collects data from PLCs and sends data to a message broker for further distribution. Data flows trigger using an API call or execute according to a schedule. Belden Horizon Data Operations supports multiple data formats.
Refer to the following formats used for data in devices.
Raw Topics
DeviceHub Tags generate a Raw Topic, which is a local topic for publishing and subscribing data through the message broker.
Belden Horizon Data Operations publishes each value to a tag-specific topic in the following topic format: devicehub.raw.{deviceID}.{tagID}.
Example of a Raw Topic
devicehub.raw.F7F72687-2F29-46E7-95E2-B5532471EBAA.2d7473c0-83a0-4174-83cc-b48a63c1b1cf
Alias Topics
When you Connect a Device, you have the option of using the Enable alias topics option. If you select to use alias topics for a device, then you won't be able to use raw topics as well. Each connected device can either use alias topics or raw topics, not both.
Important: When alias topics are enabled for a device, you can't use batch write topics. To use batch write topics, you must not select the Enable alias topics check box in the device configuration. See Connect a Device and Manage Devices for more information.
When the Enable alias topics check box is selected:
- deviceId in the raw topic format is replaced with deviceName
- tagId in the raw topic format is replaced with tagName
Alias topics use the following format: devicehub.alias.{devicename}.{tagname}.
Example of an Alias Topic
devicehub.alias.plc2.tag1
Write Topics
Write topics write data to a tag-specific topic in the following topic format: devicehub.write.{deviceID}.{tagID}. Each device instance on the devicehub.write.{deviceID}.* topic receives all messages for the corresponding device. The device instance executes a write to the specified tag on the connected device.
Example of a Write Topic
devicehub.write.F7F72687-2F29-46E7-95E2-B5532471EBAA.2d7473c0-83a0-4174-83cc-b48a63c1b1cf
Batch Write Topics
Batch write topics can send multiple write requests simultaneously in the following format: devicehub.batch_write.{deviceID}.
Important:
- Only Gen 2 drivers can use batch write topics. See the Industrial Systems Connection Guide to review available Gen 2 drivers.
- This is only available for devices that don't select the Enable Alias Topics check box in the device configuration. You must use tags in the raw topic format. See Connect a Device and Manage Devices for more information.
Example of a Batch Write Topic
devicehub.batch_write.710B913B-B915-4450-9122-8D57E803499B
Poll-Once Topics
Poll-once topics can be used to trigger a poll to a tag for data in the following topic formats:
- If raw topics are enabled: devicehub.pollonce.{deviceID}.{tagID}
- If alias topics are enabled: devicehub.pollonce.{deviceName}.{tagName}
When a poll-once topic is triggered by a message, Belden Horizon Data Operations will get data for that tag and publish a message to the raw or alias topic for that tag.
Example of a Poll-Once Topic
devicehub.pollonce.F7F72687-2F29-46E7-95E2-B5532471EBAA.2d7473c0-83a0-4174-83cc-b48a63c1b1cf
Topic Formats
The following table summarizes the types of device-level and tag-level topics, either with or without aliases. You have the option of using raw topics or alias topics.
Category | Topics | Notes |
|---|---|---|
Device | devicehub.plcstatus.{DeviceID} | Subscription to a device status |
Device | devicehub.manage.{DeviceID} | To START/STOP the device's CONNECTION |
Device | devicehub.raw.{DeviceID}.> | Publish/Subscribe to all data from a specific Device |
Device | devicehub.plcstatus.{DeviceName} | To monitor the device's CONNECTION/DISCONNECTION status with Alias topics enabled |
Device | devicehub.manage.{DeviceName} | To START/STOP the device CONNECTION with Alias topics enabled |
Device | devicehub.raw.{DeviceName}.> | A wildcard to receive messages from all tags added to the device with Alias topics enabled |
Device | devicehub.batch_write.{deviceID} | Send multiple write requests simultaneously |
Tag | devicehub.pollonce.{DeviceID}.{TagID} | Trigger this topic to get data from a tag one time |
Tag | devicehub.pollonce.{DeviceName}.{TagName} | To receive data from a poll-once raw topic with Alias topics enabled |
Tag | devicehub.raw.{DeviceID}.{TagID} | To receive data in raw format |
Tag | devicehub.write.{DeviceID}.{TagID} | To write data |
Tag | devicehub.alias.{DeviceName}.{TagName} | To receive data in raw format with Alias topics enabled |
Tag | devicehub.write.{DeviceName}.{TagName} | To write data with Alias topics enabled |
Events | system.events | Subscription to all system events |