CCU as BACnet MSTP Client

| Overview

To enhance interoperability, the 75F Central Control Unit (CCU) now supports BACnet MS/TP
(Master-Slave/Token-Passing). In addition to BACnet/IP, this enables seamless integration with a wide range of MS/TP-based field devices over RS‑485, allowing centralized monitoring, control, and data exchange across HVAC and building automation systems.

This enhancement enables the CCU to read from and optionally write to external BACnet MS/TP devices for automation.

| What is BACnet MSTP?

BACnet MS/TP is a serial communication protocol that operates over an RS‑485 network and is widely used in building automation systems. It enables reliable communication between multiple devices connected on the same bus.

In a MS/TP network:

Each device is assigned a unique MAC address.
A token is passed sequentially between master devices.
Only the device holding the token can initiate communication, ensuring orderly data exchange and preventing collisions.

| Why BACnet MSTP on the CCU?

The 75F CCU is designed as a comprehensive IoT-based Building Management Controller, capable of operating in diverse and mixed-vendor environments. To function effectively as a supervisory controller, the CCU must seamlessly integrate with a wide range of field devices and systems.

With BACnet MS/TP support, the CCU can:

Communicate with third-party controllers and field devices
Retrieve real-time data for monitoring and analytics
Write control values to support automation logic and system optimization
Integrate legacy systems operating on RS‑485 MS/TP networks

By enabling BACnet MS/TP, the CCU extends its interoperability beyond BACnet/IP, allowing it to act as a centralized BACnet supervisor for both modern and legacy devices ensuring unified monitoring, control, and data exchange across the building ecosystem.

75F CCU Integration

Within a 75F deployment:

The CCU serves as the MS/TP master, driving communication by sending read and write requests for monitoring and control.
External MS/TP devices, such as 75F MyStat MS/TP controllers, operate as subordinate devices either as masters or slaves and respond to CCU requests when addressed, enabling coordinated monitoring and control.

Role CCU MyStat

MS/TP Role Master Slave

Initiates Communication Yes Usually No

Responds to Requests Yes Yes

| Prerequisites

The 75F CCU XR is the only master device that supports the MSTP protocol.
Update the CCU to version 2.10.2 or above.
Permit the app to access various aspects, like any other app on the pop-ups for the app to work seamlessly.

Note: Only the above-mentioned versions could support a BACapp to favor the server support for BACnet BMS.

It is in this version the object instances and tagging for the haystack points are hardcoded, that can be used by a BACnet BMS.

| Installation

Remote Installation

The BACapp is part of the CCU bundle, and the bundle include the latest version of the BACapp in use, along with the home and remote apps.

To remotely install the latest version of the BACapp.

Access the system widget screen from the site overview page.
Select update BACapp from the list under the remote command drop-down as below.

Use the command with the latest version details of the BACapp, and execute the command.

You can also trigger the remote installation for BACapp from the tuner section of the internal portal as below.

Note: From the tuners section you can remotely install the BACapp for multiple CCUs at a time.

| Configuration

MSTP Dongle Setup via USB Manager

To begin BACnet MSTP communication, configure the MSTP interface using the USB Manager on the CCU.

Click Settings, then navigate to Communication.
Navigate to the Usb Manager section on the CCU interface.
Select the dongle, then choose BACnet MSTP as the protocol.

Enter the BACnet MSTP configuration.

Enter the standard BACnet MSTP supervisor settings:

Baud rate
Source address
Max masters
Max frames
Device ID

| Initialization

After the user has provided the necessary configuration details,

Click INITIALIZE.
The dongle status changes from INITIALIZE → DISABLE, indicating a successful setup (same behavior as BACnet/IP initialization).
User can view the BACnet Application Status in CCU BacApp.

| Device Pairing Workflow

Once the MSTP network interface is initialized, devices can be paired similarly to wireless zones.

Select Device Type

Navigate to the Zone Pairing section to Select Device Type.
Select Custom Equipment.
Select BACnet Equipment from the available options.

Select Device Model

To create a model, refer to the reference article BACnet based External Models Creation.
Select and search for the appropriate MSTP-enabled model.
Example: training_RTU_P

Select Communication Type

Although the CCU does not inherently recognize it as a 75F device, the UI displays both MSTP and IP Configuration options.
Select MSTP Configuration.

Choose Device Role

BACnet MSTP automatically assigns MAC addresses based on the device type:

Master devices: MAC 1–127
Slave devices: MAC 128–254

Device Discovery:

Slave devices

Assign a unique MAC address to the slave device in the salve product configuration. The supported MAC address range is 128 to 254.

After the MAC address is configured, the Master device can use this Mac address to identify and establish communication with the corresponding slave device in the CCU.

Example: The 75F HyperStat communication configuration screen shows the Address parameter set to 128, which is the MAC address assigned to the slave device. The Master device uses this address to identify and communicate with the slave device.

Refer to the following 75F HyperStat communication configuration screen for an example of a slave device configured with MAC address 128.
Select the MAC address as 128 in the MSTP Configuration to establish communication with the slave device.
Example: MAC Address 128.
Click Save.
Once the device is selected and saved, it is fully paired with the CCU.

Master devices

Select a device as the Master. The system automatically retrieves and displays the linked devices in the device list. Select the required device from the list.

Master devices support MAC addresses in the range 1 to 127.

After selecting the role, the CCU scans the MS/TP network.
All detected MS/TP devices appear in the list.
Example: TRAINING_RTUB found at MAC Address 5.
Once the device is selected and saved, it is fully paired with the CCU.

| Data Visibility and Control

After pairing:

A dynamic Zones Page is created for the MSTP device.

Select the System Status Icon to view real-time BACnet MS/TP data updates in the ZONES section.

The page updates in real time as data changes on the MS/TP network.

Typical real-time parameters include:

Occupancy (Open/Close or 1/0)
Temperatures
Setpoints
Modes
Equipment status

Users can perform the following actions:

View live sensor readings
Write values, such as heating and cooling setpoints
Observe immediate feedback on the user interface

The user experience is consistent with other 75F device integrations, with communication handled over the MS/TP network.

The BACnet MS/TP module transforms the CCU into a versatile supervisory controller capable of integrating heterogeneous building automation systems. The workflow USB Manager setup, MS/TP initialization, device discovery, and real-time data interaction provides a robust and user-friendly approach for MS/TP deployments.

| Object Instance Tagging

Favoring the above possibility, once a profile is paired, after a CCU is initialized as a BACnet server, the points created would come with a BACnet tag, to ease the detection, and points inclusion for surveying and broadcasting data by the BACnet-based BMS.

| Visualizing in BACnet Explorer

Note: Any BACnet explorer can be used to visualize the objects. In this case, we have used the YABE (Yet Another BACnet Explorer) which is a graphical program to explore and visualize BACnet devices.

Access the BACnet explorer.

Click the Add device icon to add CCU to the explorer.

The BACnet communication channel window displays.

Use the drop-down list to select the required COM port device, and configure the Baud Rate, Source Address, Max Master, and Max Frames parameters.
Click the Start button to initiate the communication.
The CCU is added to the explorer.
Click on the device to visualize the actual details of the device as per the 75F standard nomenclature.

| Portal Reading

To check the readings of each point in the portal:

Log in to Facilisight and select the site from the dropdown.
Navigate to Facilisight Assist and select Floor Planner.
Select the BACnet Zone and drag and drop it onto the floor plan.
Click Publish.
A pop-up message will appear at the bottom of the screen indicating "Success."
Navigate to Site Dashboards, click the Site Dashboard icon, and select Site Overview.
Click the BACnet Zone and scroll to Zone Settings.