FCU Master-Slave Configuration

The FCU controller can work in networks, where one device is a master and the remaining devices are slaves. This function is useful if there are more than one devices working in a single room. In this case, only the master device can work with the room panel and control from the BMS. All other devices in the room follow the master parameters creating the network. In the default application the master-slave grouping is activated automatically if the master and slaves have been set with the right BACnet Device ID. A single network can contain up to 6 devices, 1 master and up to 5 slaves.

WARNING! This function is available only in the BACnet protocol, and it works without a supervisor. In the Modbus protocol, master-slave function must be provided by supervisor.

FCU Addressing MAC and ID

The FCU controller’s MAC Address is set using the MAC DIP switch. The BACnet ID of the device is a combination of the device manufacture number and MAC address, where the first 3 digits contain manufacture number and the next 3 digits contain MAC address.

Example: Configuration how to set the FCU controller MAC address 83. Device’s manufacture BACnet number is 826.

The MAC address 83 contains the following multiplicity of number 2: 83 = 1 + 2 + 16 + 64. The DIP switch address settings is shown in table below. All addresses of the DIP switch configuration are presented in table at the end of this document.

In this case the BACnet ID will be: 826 083.

Auto Binding Addressing

The default application allows for automatic calculation of the BACnet Device Id of slave devices in the BACnet Master Slave Network, depending on the BACnet Device ID of master devices. This function is called auto-binding. The table below presents the values of master BACnet Device Id and corresponding BACnet Device Id of slave devices for auto-binding function:

The auto-binding function can be disabled (by setting the true value to the Local Remote Auto Binding network variable). In this case, Id of slave devices have to be set by the user (in network parameters: Remote Slave 1 Device Id-Remote Slave 5 Device Id).

Master-Slave Sharing Parameters

If the master device detects that it can communicate with a slave device, it sends/receives the following network parameters:

In the auto-binding function the sharing parameters have the following properties:

• Net_Temperature: sends the room temperature from the master device to slave devices. The slave devices can work without connected temperature sensor (CGF DIP switches number 5 and 6 in on position);
• Setpoint: the setpoint for slave devices, based on the master device’s setpoint and the Setpoint_Offset value. This parameter does not include the Unoccupied_Offset and Standby_Offset, Effective Setpoint is calculated in the slave device according to the FCU mode;
• Occupancy_Mode: the occupancy mode for slave devices, based on the master device Occupancy_Status value;
• Fcu_Mode: the FCU_Mode for slave devices, based on the master device’s FCU_Mode value;
• Fan_Mode: the Fan_Mode for slave devices, based on the master device’s Fan_Mode value;
• Slave_Window_Status: every 1 minute the master device checks the slave device’s open window status. If the master device detects that the window is open (their own or one of the devices in group), it runs the open window function (waits the time defined in the Window_Status_Delay network variable, and if the window is still open, switches off the whole group).

Application Status

In order to give the user possibility to troubleshoot and diagnose application’s operation, the App_status network variable was added. The information is represented as a multistate value available in the Modbus register 99 and the BACnet Device object property 5002. This network variable allows to understand, what is causing a problem if the application is not working, or which fault it has gone into. It also shows transitional states such as yield, restart, and hibernate.