| Overview
As part of enhancing the interoperability capabilities of the 75F Building Management System, support for BACnet MSTP (Master-Slave/Token-Passing) has been added to the CCU. While the CCU already supports BACnet/IP communication, MSTP support enables seamless integration with a wide range of MSTP-based field devices, sensors, controllers, and third-party equipment commonly used in legacy and modern building automation environments.
With this enhancement, the CCU can now read data points from external BACnet MSTP devices and optionally write control values as part of its automation logic.
| Why BACnet MSTP on the CCU?
The CCU is positioned as a complete IoT-based Building Management Controller. For it to function as a supervisory device within mixed-vendor environments, it must:
Communicate with third-party controllers and devices.
Fetch real-time values for monitoring.
Write data for control operations and algorithm execution.
Integrate legacy systems that operate on MSTP networks.
By introducing MSTP support, the CCU can now act as a BACnet supervisor/master for devices that do not support BACnet/IP.
| What is BACnet MSTP?
BACnet MSTP (Master-Slave/Token-Passing) is a serial communication protocol typically operating over RS-485. In MSTP networks:
Devices are assigned MAC addresses.
A token circulates among master devices.
Only the device holding the token is allowed to initiate communication.
For 75F’s integration:
The CCU operates as the MSTP Master, initiating all read and write requests.
The external MSTP devices (e.g., HyperStat MSTP) operate as slave or subordinate devices, responding only when addressed.
| MSTP Dongle Setup via USB Manager
To begin MSTP communication, the user configures the MSTP interface through the USB Manager on the CCU.
Identify the MSTP USB Dongle
Navigate to USB Manager.
Locate the connected MSTP dongle.
Select the dongle and choose BACnet MSTP as its protocol.
Enter MSTP Configuration
Enter standard BACnet MSTP supervisor settings:
Baud rate
MAC address of the CCU (as master)
Max masters
Max info frames
Network ID
Once the configuration is complete,
Click Initialise.
The dongle status changes from Disabled → Initialised, indicating successful setup (same behaviour as BACnet/IP initialisation).
| Device Pairing Workflow
Once the MSTP network interface is initialised, devices can be paired similarly to wireless zones.
Select Device Type
Navigate to the zone pairing section.
Choose Custom Equipment.
Select BACnet Equipment from the available options.
Select Device Model
Choose the appropriate MSTP-enabled model.
Example: HyperStat MSTP
Select Communication Type
Although the CCU does not inherently know it is a 75°F device:
The UI displays both MSTP and IP options.
Select MSTP.
Choose Device Role
BACnet MSTP auto-assigns MAC addresses based on device type:
Master devices: MAC 1–127
Slave devices: MAC 128–254
Device Discovery
After selecting the role:
The CCU scans the MSTP network.
All detected MSTP devices appear in the list.
Example: HyperStat found at MAC Address 4
Once selected and saved, the device is fully paired with the CCU.
| Data Visibility and Control
After pairing:
A dynamic Zones Page is created for the MSTP device.
The page updates in real time as data changes on the MSTP network.
Typical real-time parameters include:
Occupancy (Open/Close or 1/0)
Temperatures
Setpoints
Modes
Equipment states
Users can:
View live sensor readings.
Write values like heating/cooling setpoints.
Observe immediate feedback on the UI.
The experience is identical to other 75F device integrations, but via MSTP.
The BACnet MSTP module transforms the CCU into a versatile supervisory controller capable of integrating heterogeneous building automation systems. The workflow—USB Manager setup, MSTP initialisation, device discovery, and real-time data interaction—provides a robust and user-friendly method for MSTP deployments.
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