CCU as BACnet MSTP Server

| Overview

The Central Control Unit (CCU) extends the interoperability capabilities of the 75F ecosystem by supporting BACnet MSTP (Master-Slave/Token-Passing) Server functionality. Through this capability, the CCU exposes 75F devices, zones, equipment points, alarms, schedules, and operational data as standard BACnet objects over an RS-485 BACnet MSTP network.

This allows legacy Building Management Systems (BMS), supervisory controllers, and BACnet MSTP masters to seamlessly discover, monitor, and control the 75F ecosystem without requiring BACnet/IP connectivity.

The CCU acts as a BACnet MSTP Server device on the RS-485 trunk, making 75F data available to third-party BACnet clients while maintaining secure and reliable communication with the 75F platform.

| Why BACnet MSTP on the CCU?

Many building automation deployments continue to rely on BACnet MSTP networks due to their simplicity, reliability, and extensive installed base.

BACnet MSTP Server support enables the CCU to:

• Integrate with legacy BACnet MSTP BMS systems.
• Expose 75F data without requiring BACnet/IP infrastructure.
• Support mixed BACnet/IP and BACnet MSTP environments.
• Enable centralized monitoring and control through existing BAS platforms.
• Extend the reach of the 75F ecosystem into brownfield installations.

This capability allows facility managers to continue using their existing MSTP infrastructure while leveraging the intelligence and optimization capabilities of the 75F platform.

| What is BACnet MSTP?

BACnet MSTP (Master-Slave/Token-Passing) is a BACnet communication protocol operating over RS-485 serial networks.

In an MSTP network:

• Master devices participate in token passing.
• Only the device holding the token may initiate communication.
• Slave devices respond only when addressed.
• Communication occurs over a shared RS-485 trunk.

Key characteristics include:

• Token-passing communication mechanism.
• Multi-drop RS-485 architecture.
• Device communication through MAC addressing.
• Deterministic network access.
• Reliable communication in electrically noisy environments.

• Devices are assigned MAC addresses.

• A token circulates among master devices.

• Only the device holding the token is allowed to initiate communication.

| Prerequisite 

The MSTP capability is only available on the XR. The Iproda table does not support MSTP server capability.

| MSTP Interface Configuration

The BACnet MSTP interface is configured through the USB Manager.

Step 1: Connect MSTP Dongle

Connect the BACnet MSTP USB-to-RS485 interface to the CCU.

Navigate to:

Settings → USB Manager

Select:

BACnet MSTP

Step 2: Configure MSTP Parameters

Configure the following parameters:

Step 3: Initialize MSTP Service

After configuration:

1. Click Initialize.
2. Verify MSTP service status.
3. Confirm successful RS-485 communication.

The service status changes from:

Disabled → Initialized

indicating that BACnet MSTP communication is active.

| Data Flow

The CCU aggregates information from paired 75F devices and publishes the information as BACnet objects for external consumption.

| Device Objects

Each CCU appears as a BACnet Device Object containing:

• Device Name
• Device Instance
• Vendor Information
• Location
• Description

| Device Discovery

BACnet MSTP masters can discover the CCU using standard BACnet services.

Supported services include:

• Who-Is
• I-Am
• Read Property
• Read Property Multiple
• Write Property
• Device Discovery

Once discovered, BACnet clients can browse the exposed BACnet object hierarchy.

| Read and Write Support

The BACnet Server supports both monitoring and control operations.

Read Operations

BACnet clients can:

• Read temperatures
• Read occupancy status
• Read equipment state
• Read alarms
• Read schedules
• Read sensor values

Write Operations

Where permitted, BACnet clients can:

• Modify cooling setpoints
• Modify heating setpoints
• Change fan modes
• Adjust occupancy commands
• Update operational modes

| BACnet Explorer Verification

The server can be validated using BACnet Explorer tools such as YABE.

Verification Steps:

• Open BACnet Explorer.

• Select local network adapter.

• Start BACnet communication.

• Discover devices.  
• Locate CCU BACnet device.

• Verify point visibility.

• Test read/write functionality.

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.

More information on CCU as BACnet Server object list, refer to the attachment.