L2003592-F Modbus TCP
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Specifications
- Product Name: Duco Connectivity Board
- Supported Models: DucoBox Silent Connect, DucoBox Focus,
DucoBox Energy - Modbus Subset Support: HEX 0x03, 0x04, 0x06, 0x10
- Modbus Component Interface: TCP on port 502
Product Usage Instructions
Working with Registers/Parameters
The DucoBox Silent Connect, Focus, and Energy support the
following Modbus subset functions:
- Read multiple HOLDING registers (HEX 0x03)
- Read multiple INPUT registers (HEX 0x04)
- Write single HOLDING register (HEX 0x06)
- Write multiple HOLDING registers (HEX 0x10)
Input registers are read-only 16-bit variables, while holding
registers are read/write 16-bit variables. The Modbus address can
be set via the Display menu, Duco Installation App, or Duco Network
Tool.
Communication with Control Unit
The external control unit communicates with each component
through read parameters (INPUT) and write parameters (HOLDING).
Read Parameters (INPUT): Ventilation system
type, ventilation status, indoor air quality based on relative
humidity, indoor air quality based on CO2 value, etc.
Write Parameters (HOLDING): Ventilation status,
component identification, etc.
It is recommended to read the current value before performing a
write action to adjust the value. There are limits on write actions
to prevent excessive writing.
Overview of Parameters
Below is an overview of INPUT and HOLDING parameters for the
ventilation system and its components:
| Register | INPUT (Read Parameter) | Data Conversion | Application | Recommended Survey Frequency |
|---|---|---|---|---|
| 0020 | Temperature ODA | Displays the temperature of the supply air from outside to the unit (Outdoor Air). | DucoBox Energy | 1/min |
Frequently Asked Questions (FAQ)
Q: How can I set the Modbus address for the Duco Connectivity
Board?
A: The Modbus address can be set via the Display menu, Duco
Installation App, or Duco Network Tool.
Q: What are the limits on write actions for the Duco
Connectivity Board?
A: There is a daily limit of 200 write actions, with additional
actions allowed based on the number of supply or extraction zones.
Additionally, there is a periodic limit of one write action every 2
seconds.
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Information sheet
Modbus TCP
L2003592-F 18.07.2025
01 Introduction
The Modbus interface on DUCO systems (via the Duco Connectivity Board option on a DucoBox)1 allows an external controller or building management system to communicate with the DUCO ventilation system. That way, you can retrieve info about the ventilation network via read parameters or input registers, or read or adjust settings via write parameters or holding registers. The supported protocol is Modbus TCP over Ethernet or Wi-Fi via the Duco Connectivity Board. The information in this document is valid from API version v2.5 onwards.
1
Duco Connectivity Board option only possible on DucoBox Silent Connect, DucoBox Focus and DucoBox Energy (all variants).
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
02 Working with registers / parameters
The DucoBox Silent Connect, Focus and Energy support the following Modbus subset:
HEX 0x03 0x04 0x06 0x10
DEC SUPPORT FUNCTION
3
Read multiple HOLDING registers
4
Read multiple INPUT registers
6
Write single HOLDING register
16 Write multiple HOLDING registers
Here, input registers are 16-bit read-only variables and holding registers are 16-bit read/write variables. Combined consecutive registers are not used. The Duco Connectivity Board functions as a Modbus component via TCP on port 502. The Modbus address can be set via the Display menu (see information sheet L8000002), the Duco Installation App or the Duco Network Tool.
The external control unit communicates with each component (node) through read parameters (INPUT) and write parameters (HOLDING). Read parameters (INPUT): ventilation system type, ventilation status, indoor air quality based on relative humidity, indoor air
quality based on CO2 value, … Write parameters (HOLDING): ventilation status, identification (of components), …
Note: Read parameters can be read without restriction. There are, however, two important limits to write actions: 1. a daily limit of 200 write actions. From a second supply or extraction zone, 100 write actions are added per additional zone. 2. a periodic limit of one write action every 2 seconds.
It is recommended to use a logic that first reads the current value before determining whether a new write action is needed to adjust the value.
Each node and its parameters are assigned a code: XXyy (XX=node number, yy=parameter number).
parameter number node number
xx07
INPUT REGISTER
xx06
xx07
INPUT
(read parameter)
DATA
CONVERSION
Ventilation status Indicates the status of ventilation
Filter Time Remaining Indicates remaining filter life
0 = OK 1 = Error 2 = Inactive
Days
This allows all values to be read and controlled from the external control unit. There are specific parameters for each component.
Due to a difference in some Modbus implementations compared to the official specification (on which our implementation is based), an address shift of `1′ may occur for the read and write parameters. E.g.: read address `20′ will become `19′. For any box type (Silent Connect, Focus, Energy), this can be resolved via the Duco Installation App or the Duco Network Tool under tab > Tree view-Settings-external settings. With the DucoBox Focus, moreover, this can be solved by setting ‘ > ‘RegOffs’ to ‘1’ under > CONFIG > Modbus in the Display menu. With the DucoBox Energy also via ‘Register Offset’ under > Setting > Modbus in the advanced menu.
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
03 Overview of parameters
The overview is grouped into three sections: · Parameters that are only supported at the system level. · Parameters that are only supported by the DucoBox. · Parameters that are supported by the nodes (components).
Below is an overview of the INPUT and HOLDING parameters for both the ventilation system and the components.
System parameters:
Register
INPUT (read parameter)
Data
Conversion
Application
Recommended survey frequency
0020
Temperature ODA Displays the temperature of the supply air from outside
to the unit (Outdoor Air).
°C / 10
DucoBox Energy
1 / min
0021 0022 0023
SUP temperature Displays the temperature of the supply air from the unit
to the home (Supply Air).
Temperature ETA Displays the temperature of the exhaust air from the home to the unit (Extract
Air).
Temperature EHA Displays the temperature of the exhaust air from the unit to the outside (Exhaust
Air).
°C / 10 °C / 10 °C / 10
DucoBox Energy
1 / min
DucoBox Energy
1 / min
DucoBox Energy
1 / min
0024
Outdoor temperature Measured via the weather
station.
°C / 10
DucoBox with weather station
1 / min
0025
Wind speed Measured via the weather
station.
Decimetre/second
DucoBox with weather station
1 / min
0026
Rain Measured via the weather
station.
0 = No (False) 1 = Yes (True)
DucoBox with weather station
1 / min
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
Register
INPUT (read parameter)
Data
Conversion
0027
Light intensity south Measured via the weather
station.
Kilolux
Application
Recommended survey frequency
DucoBox with weather station
1 / min
0028
Light intensity east Measured via the weather
station.
Kilolux
DucoBox with weather station
1 / min
0029
Light intensity west Measured via the weather
station.
Kilolux
DucoBox with weather station
0030
Local API Version Displays the local API
version.
Whole number Example: 2.4 becomes 204. Public API version ‘X.Y’ becomes
Modbus = X · 100 + Y
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
0031
Remaining write actions Displays the number of
corrective commands until midnight.
Whole number
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
Negative temperatures are displayed as a number greater than 32767. To display this value correctly, you need to implement some logic to convert the value. The formula is: (value-65536)/ 10
Example: If(ModBusInputRegisterValue >= 32768)
Temp = (ModbusInputRegisterValue 65536)/10 Else
Temp = ModbusInputRegisterValue/10 End
1 / min 1 / day 1 / min
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
DucoBox parameters:
Register
Data
INPUT (read parameter)
Conversion
0100 0102 0103 0104
0105
System type Indicates the type of ventilation system
Remaining time Current Ventilation mode
Indicates the remaining time the DucoBox will ventilate in this mode Flow rate versus target
level Displays the actual ventilation mode for the zone in which the component is located
Indoor air quality based on RH
Average indoor air quality based on measured relative
humidity
Indoor air quality based on CO2
Average indoor air quality based on measured CO2
value
17 = DucoBox Seconds
Percentage
100 % Very good indoor air 95 % quality
90 % 80 % Good indoor air quality 65 %
50 % Temporarily acceptable 35 % indoor air quality
20 % 5 %
Poor indoor air quality
100 % 95 % 90 %
Very good indoor air quality
85 % 80 % Good indoor air quality 75 %
70 % 65 % 60 % 55 % 50 %
Temporarily acceptable indoor air quality
45 % 40 % 35 % 35 %
Poor indoor air quality
Application
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
Recommended survey frequency
one-time
1 / min
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
1 / min
Box sensor DucoBox Silent
Connect Box sensor DucoBox Energy
1 / min
Box sensor DucoBox Silent
Connect Box sensor DucoBox Energy
1 / min
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
Register
INPUT (read parameter)
Data
Conversion
0106 0107
Ventilation status Indicates the status of
ventilation
Filter Time Remaining Indicates remaining filter
life
0 = OK 1 = Error 2 = Inactive
Days
Application
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
Recommended survey frequency
1 / min
DucoBox Energy
1 / day
0108 0109
Filter status Indicates the status of the
filter
Humidity Indicates the measured
humidity value.
0 = OK 1 = Filter is dirty
2 = Inactive
RH (%) (relative humidity)
10 % 15 %
Poor indoor air quality
20 % Temporarily acceptable 25 % indoor air quality
30 % 35 % 40 %
45 % 50 % 55 %
60 % 65 % 70 %
Good indoor air quality
Very good indoor air quality
Good indoor air quality
75 % Temporarily acceptable 80 % indoor air quality
85 % Poor indoor air quality
DucoBox Energy
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
+ minimum 1 humidity sensor
1 / min 1 / min
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
INPUT (read parameter)
Register
0110
Data
Conversion
CO2 Indicates the measured
CO2 value .
CO2 (ppm)
< 800 800 900
Very good indoor air quality
1000 1100 Good indoor air quality 1200
1250 1300 1350 1400 1450
Temporarily acceptable indoor air quality
1500
1550 1600
Poor indoor air quality
> 1600
HOLDING (read/write parameter)
Register
Data
Conversion
0100 xx01
Ventilation mode Here, the ventilation mode can be
adjusted.
Conversion 11 through 16 is used to maintain manual modes longer.
For example: Manual 1 (conversion 4) is set to duration t by default. For Manual 1 x 2 (conversion 11), the mode t x 2 (= 2 x standard duration) will be maintained and for Manual 1 x 3 (conversion 14), the mode t x 3 (= 3 x standard duration) will be maintained.
Identification Here, a component can be identified. This will light up
blue.
0 = AUTO 4 = Manual 1 5 = Manual 2 6 = Manual 3 7 = Not at home 8 = Permanent 1 9 = Permanent 2 10 = Permanent 3 11 = Manual 1 x 2 12 = Manual 2 x 2 13 = Manual 3 x 2 14 = Manual 1 x 3 15 = Manual 2 x 3 16 = Manual 3 x 3
0 = Node Visualisation OFF 1= Node Visualisation ON
Application
Recommended survey frequency
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
+ minimum 1 CO2 Sensor
1 / min
Application
Recommended survey frequency
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
1 / min
DucoBox Silent Connect
DucoBox Focus DucoBox Energy
One-time, read before write. (Read and check before write)
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
Register
0102 0103 0104 0105
HOLDING (read/write parameter)
Data
Supply temperature target zone 1
Here, the comfort temperature of the SUP zone 1 can be adjusted
Supply temperature target zone 2
Here, the comfort temperature of the SUP zone 2 can be adjusted
Supply temperature target zone 3
Here, the comfort temperature of the SUP zone 3 can be adjusted
Supply temperature target zone 4
Here, the comfort temperature of the SUP zone 4 can be adjusted
Conversion
°C / 10 °C / 10 °C / 10 °C / 10
Application
DucoBox Energy DucoBox Energy DucoBox Energy DucoBox Energy
Recommended survey frequency
One-time, read before write. (Read and check before write)
One-time, read before write. (Read and check before write)
One-time, read before write. (Read and check before write)
One-time, read before write. (Read and check before write)
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
Node parameters:
INPUT (read parameter)
Register
Data
xx00
System type Indicates the type of ventilation system
xx02 xx03
Remaining time Current Ventilation mode
Indicates the remaining time the DucoBox will ventilate in this mode
Flow rate versus target level
Displays the actual ventilation mode for the zone in which the component is located
Conversion
Application
0 = Unknown 7 = DucoTronic window ventilator
8 = User controller RF/BAT 9 = User controller RF/Wired 10 = Humidity Room sensor
12 =CO2 Room sensor 13 = Sensorless Control Valve 14 = Humidity Control Valve
16 = CO2 Control Valve 18 = Switch Sensor
22 = iAV Control valve 23 = iAV Humidity 25 = iAV CO2 27 = Control unit
28 =CO2/RH control valve 29 = User Controller `Sun Control’ 30 = User Controller `Ventilative
Cooling’ 31 = External multi-zone valve
35 = Humidity box sensor 37 = CO2 Box Sensor 38 = Motor relay
39 = Duco Weather Station or Outdoor Temperature Sensor
40 = Modbus motor 41 = Digital input 42 = Digital output 44 = Modbus relay 45 = Perilex 46 = Relay output
Seconds
User controller Room sensor Box sensor Control valve Switch sensor Electronic window
ventilator
User controller Room sensor Control valve Switch sensor
Percentage
Control valve Electronic window
ventilator
Recommended survey frequency
one-time
1 / min 1 / min
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
Register
xx04 xx05
xx09
INPUT (read parameter)
Data
Conversion
Indoor air quality based on RH
Average indoor air quality based on measured relative
humidity
Indoor air quality based on CO2
Average indoor air quality based on measured CO2
value
Humidity Indicates the measured
humidity value.
100 % Very good indoor air 95 % quality
90 % 80 % Good indoor air quality 65 %
50 % Temporarily acceptable 35 % indoor air quality
20 % Poor indoor air quality
100 % 95 % 90 %
Very good indoor air quality
85 % 80 % Good indoor air quality 75 %
70 % 65 % 60 % 55 % 50 %
Temporarily acceptable indoor air quality
45 % 40 % 35 % 30 %
Poor indoor air quality
RH (%) (relative humidity)
10 % 15 %
Poor indoor air quality
20 % Temporarily acceptable 25 % indoor air quality
30 % 35 % 40 %
45 % 50 % 55 %
60 % 65 % 70 %
Good indoor air quality
Very good indoor air quality
Good indoor air quality
75 % Temporarily acceptable 80 % indoor air quality
85 % Poor indoor air quality
Application
Recommended survey frequency
Room sensor Control valve
1 / min
Room sensor Control valve
1 / min
Humidity Room Sensor
Humidity Box Sensor
Humidity Control Valve
Electronic window ventilator
1 / min
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
INPUT (read parameter)
Register
xx10
Data
Conversion
CO2 Indicates the measured
CO2 value .
CO2 (ppm)
< 800 800 900
Very good indoor air quality
1000 1100 Good indoor air quality 1200
1250 1300 1350 1400 1450
Temporarily acceptable indoor air quality
1500
1550 1600
Poor indoor air quality
> 1600
HOLDING (read/write parameter)
Register
Data
Conversion
xx00 xx01
Ventilation mode Here, the ventilation mode can be
adjusted.
Conversion 11 through 16 is used to maintain manual modes longer.
For example: Manual 1 (conversion 4) is set to duration t by default. For Manual 1 x 2 (conversion 11), the mode t x 2 (= 2 x standard duration) will be maintained and for Manual 1 x 3 (conversion 14), the mode t x 3 (= 3 x standard duration) will be maintained.
Identification Here, a component can be identified. This will light up
blue.
0 = AUTO 4 = Manual 1 5 = Manual 2 6 = Manual 3 7 = Not at home 8 = Permanent 1 9 = Permanent 2 10 = Permanent 3 11 = Manual 1 x 2 12 = Manual 2 x 2 13 = Manual 3 x 2 14 = Manual 1 x 3 15 = Manual 2 x 3 16 = Manual 3 x 3
0 = Node Visualisation OFF 1= Node Visualisation ON
Application
Recommended survey frequency
CO2 Room Sensor CO2 Box Sensor CO2 Control Valve
1 / min
Application
Recommended survey frequency
User controller Room sensor Box sensor Control valve Electronic window
ventilator
1 / min
User controller Room sensor Control valve Switch sensor Electronic window
ventilator
One-time, read before write. (Read and check before write)
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L2003592 -F 18.07.2025 Information sheet ModBus TCP
04 General data
To find out which nodes are present in the network, you can (optionally) use the INPUT registers below. Alternatively, you can scan all registers.
Example:
Example: Response to input register 0001:
INPUT REGISTER
0000 0001 0002 0003 0004 0005 0006 0007 0008
DATA
Bit field indicating which node numbers between 1 and 15 are occupied in the network Bit field indicating which node numbers between 16 and 31 are occupied in the network Bit field indicating which node numbers between 16 and 31 are occupied in the network Bit field indicating which node numbers between 48 and 63 are occupied in the network Bit field indicating which node numbers between 64 and 79 are occupied in the network Bit field indicating which node numbers between 80 and 95 are occupied in the network Bit field indicating which node numbers between 96 and 111 are occupied in the network Bit field indicating which node numbers between 112 and 127 are occupied in the network Bit field indicating which node numbers between 128 and 143 are occupied in the network
0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1
Node 16 is present in the network Node 17 is not present in the network Node 18 is present in the network …
REGISTER
DATA
0000 0001 0002 0003 0004 0005 0006 0007 0008
Bit field indicating which node numbers between 1 and 15 are occupied in the network Bit field indicating which node numbers between 16 and 31 are occupied in the network Bit field indicating which node numbers between 16 and 31 are occupied in the network Bit field indicating which node numbers between 48 and 63 are occupied in the network Bit field indicating which node numbers between 64 and 79 are occupied in the network Bit field indicating which node numbers between 80 and 95 are occupied in the network Bit field indicating which node numbers between 96 and 111 are occupied in the network Bit field indicating which node numbers between 112 and 127 are occupied in the network Bit field indicating which node numbers between 128 and 143 are occupied in the network
RECOMMENDED SURVEY FREQUENCY
one-time
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Documents / Resources
 | DUCO L2003592-F Modbus TCP [pdf] Instruction Manual Silent Connect, Focus, Energy, L2003592-F Modbus TCP, L2003592-F, Modbus TCP, TCP |