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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.

AddressS1S2S3S4S5S6S7S8
83OnOn

On
On
Address 83 DIP switch configuration

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:


Master Id

Slave 1 ID

Slave 2 ID

Slave 3 ID

Slave 4 ID

Slave 5 ID

826101

826001

826002

826003

826004

826005

826102

826006

826007

826008

826009

8260010

826103

826011

826012

826013

826014

826015

826104

826016

826017

826018

826019

826020

826105

826021

826022

826023

826024

826025

826106

826026

826027

826028

826029

826030

826107

826031

826032

826033

826034

826035

826108

826036

826037

826038

826039

826040

826109

826041

826042

826043

826044

826045

826110

826046

826047

826048

826049

826050

826111

826051

826052

826053

826054

826055

826112

826056

826057

826058

826059

826060

826113

826061

826062

826063

826064

826065

826114

826066

826067

826068

826069

826070

826115

826071

826072

826073

826074

826075

826116

826076

826077

826078

826079

826080

826117

826081

826082

826083

826084

826085

826118

826086

826087

826088

826089

826090

826119

826091

826092

826093

826094

826095

826120

826096

826097

826098

826099

826100

Other

0

0

0

0

0

Master Slave Id - 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:

Network Variable NameUnitsAccessBACnet BV IDBACnet AV IDModbus CoilModbus RegisterDefault ValueDirection

Net_Temperature

°C

RW

-

6

-

106

21

To Slave

Setpoint

°C

RW

-

1

-

101

21

To Slave

Occupancy_Mode

N/A

RW

-

0

-

100

1

To Slave

Fcu_Mode

N/A

RW

-

4

-

104

1

To Slave

Fan_Mode

N/A

RW

-

3

-

103

0

To Slave

Slave_Window_Status

Bool

RW

69

-

1269

-

true

To Master

Master-slave sharing 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).

Name

Units

Access

BACnet BV ID

BACnet AV ID

Modbus Coil

Modbus Register

Default Value

Local_Remote_Auto_Binding

Bool

RW

9

-

1209


False

Remote_Slave1_Device_ID

N/A

RW

-

54

-

154

0

Remote_Slave2_Device_ID

N/A

RW

-

56

-

156

0

Remote_Slave3_Device_ID

N/A

RW

-

58

-

158

0

Remote_Slave4_Device_ID

N/A

RW

-

60

-

160

0

Remote_Slave5_Device_ID

N/A

RW

-

62

-

162

0

Slave1_Active

Bool

RO

96

-

1296

-

N/A

Slave2_Active

Bool

RO

97

-

1297

-

N/A

Slave3_Active

Bool

RO

98

-

1298

-

N/A

Slave4_Active

Bool

RO

99

-

1299

-

N/A

Slave5_Active

Bool

RO

100

-

1300

-

N/A

Master device network parameters dedicated to master-slave function

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.

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