KNX Bus Devices: KNX Basic exam questions with worked answers

Practice questions from the KNX Bus Devices block of the KNX Basic certification. Detailed corrections, public sources, free to read without sign-up.

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Questions for the "KNX Bus Devices" topic

Q01
A functioning KNX bus device principally consists of three interconnecting parts: a bus coupling unit (BCU), an application module (AM) and an application program (AP).
TrueFalse
KNX Bus Devices· Bus device components & function· Easy
Correct answer
True
Learning tip
The source states a functioning bus device principally consists of these three interconnecting parts.
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Q02
From an electronics point of view, which two elements are integrated together to form a regular bus coupling unit (BCU)?
- A.The application module and the application program
- B.The transceiver and the microcontroller
- C.The transceiver and the digital-analog converter
- D.The programming button and the programming LED
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
B — The transceiver and the microcontroller
Learning tip
Correct: The text says the transceiver and microcontroller are integrated in a regular BCU whose electronics cannot be separated.
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Q03
What are the two functions of the Physical External Interface (PEI) between a separated application module and bus coupling unit?
- A.Assigning the individual address and storing the application program
- B.Connecting the device to the KNX bus and supplying the full mains voltage
- C.Exchanging messages between the two parts and providing limited power to the application module
- D.Converting digital signals to analog and amplifying telegrams
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
C — Exchanging messages between the two parts and providing limited power to the application module
Learning tip
Correct: The text lists exactly these two functions of the PEI.
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Q04
When a bus coupling unit and an application module are bought as separate components, what does the KNX documentation require regarding their origin?
- A.They may be freely combined from any KNX-certified manufacturers
- B.They only need to share the same medium (TP or RF)
- C.The BCU may be any brand but the AM must be KNX Association branded
- D.They must always be sourced from the same manufacturer
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
D — They must always be sourced from the same manufacturer
Learning tip
Correct: The text states the BCU and AM must always be sourced from the same manufacturer.
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Q05
How are the bus coupling unit and application module usually arranged in a DIN rail-mounted KNX device?
- A.Inseparably connected together in one housing
- B.Always separated and joined through an external PEI
- C.As two DIN modules from different manufacturers
- D.Connected only by the KNX bus cable
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
A — Inseparably connected together in one housing
Learning tip
Correct: The text states DIN rail-mounted devices usually integrate the BCU and AM inseparably in one housing.
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Q06
When a sensor's application module and bus coupling unit are physically separated (mainly with flush-mounted sensors), how are they connected?
- A.Only through the standardized KNX bus connector
- B.Through a standardized or manufacturer-specific Physical External Interface (PEI)
- C.Wirelessly via KNX-RF
- D.By soldering the application program onto the BCU
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
B — Through a standardized or manufacturer-specific Physical External Interface (PEI)
Learning tip
Correct: The text says the application module can be connected to the BCU via a standardized or manufacturer-specific PEI.
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Q07
Inside an integrated KNX product, what is the role of the electronic circuit called the 'transceiver'?
- A.It runs the operating software and the application program
- B.It executes the application function such as switching a load
- C.It takes care of coupling to the medium and is responsible for sending and receiving telegrams
- D.It stores the individual address and group addresses
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
C — It takes care of coupling to the medium and is responsible for sending and receiving telegrams
Learning tip
Correct: The text defines the transceiver as the circuit handling the coupling function to the medium, responsible for sending and receiving telegrams.
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Q08
Why is KNX described as a decentralized system that needs no central supervising unit?
- A.Because a central computer continuously supervises all devices
- B.Because all telegrams are routed through a mandatory master controller
- C.Because the power supply stores the application program for every device
- D.Because each bus device has its own intelligence from an integrated operating system and program memory
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
D — Because each bus device has its own intelligence from an integrated operating system and program memory
Learning tip
Correct: The text says each device's own intelligence is why KNX is decentralized and needs no central unit.
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Q09
How is a TP (Twisted Pair) device usually connected to the KNX bus?
- A.Via the standardized bus connector, colour-coded dark grey/red
- B.Via a Physical External Interface (PEI)
- C.Via a mains plug at 230 V
- D.Via a white/yellow bus connector
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
A — Via the standardized bus connector, colour-coded dark grey/red
Learning tip
Correct: The text says TP devices connect to the bus mostly via the standardized bus connector (dark grey/red).
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Q10
What is the purpose of putting a KNX device into programming mode with its programming button?
- A.To switch the connected electric load on or off
- B.To provide power to the application module
- C.To allow assignment of the device's individual address
- D.To couple the device to the bus medium
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
C — To allow assignment of the device's individual address
Learning tip
Correct: The text equates programming mode with assignment of the individual address.
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Q11
For which two media are KNX bus coupling units currently available?
- A.Twisted Pair and Powerline
- B.Ethernet (KNXnet/IP) and RF
- C.RF and Powerline
- D.Twisted Pair (SELV) and RF (KNX-RF)
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
D — Twisted Pair (SELV) and RF (KNX-RF)
Learning tip
Correct: The text says BCUs are available for two media, Twisted Pair (SELV) and RF (KNX-RF).
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Q12
Depending on their main function, bus devices are basically divided into just two classes: sensors and actuators.
TrueFalse
KNX Bus Devices· Bus device components & function· Easy
Correct answer
False
Learning tip
The text lists three classes: sensors, actuators and controllers, not two.
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Q13
Why is it rare nowadays to have a device with pure sensor or pure actuator functionality?
- A.Because controllers have replaced all sensors and actuators
- B.Because, for example, a push button with LED status display also has an actuator function and an actuator with status information also has a sensor function
- C.Because every device must contain a digital-analog converter
- D.Because pure sensors are not allowed on Twisted Pair
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
B — Because, for example, a push button with LED status display also has an actuator function and an actuator with status information also has a sensor function
Learning tip
Correct: The text gives exactly these examples of devices combining both roles.
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Q14
Which sequence correctly describes how a KNX sensor works?
- A.The BCU receives a telegram from the bus and the application module switches a load
- B.The application module sends telegrams directly onto the bus without the BCU
- C.The application module reports its inputs to the BCU, which codes the data and sends it on the bus
- D.The controller reads the inputs and the sensor regulates the actuators
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
C — The application module reports its inputs to the BCU, which codes the data and sends it on the bus
Learning tip
Correct: This is the sensor data path stated in the text.
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Q15
What does the bus coupling unit of an actuator do when a telegram arrives from the bus?
- A.It codes the state of its inputs and sends a new telegram on the bus
- B.It regulates the interaction between other sensors and actuators
- C.It assigns itself an individual address
- D.It decodes the telegram and passes the information to the application module, which executes the command
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
D — It decodes the telegram and passes the information to the application module, which executes the command
Learning tip
Correct: The text says the actuator's BCU receives and decodes telegrams and passes them to the AM, which executes the command.
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Q16
Which statement correctly characterises a KNX controller?
- A.It regulates the interaction between sensors and actuators and has no physical inputs or outputs
- B.It detects physical variables and reports its inputs on the bus
- C.It receives telegrams and switches an electric load
- D.It supervises the whole installation as a central computer
KNX Bus Devices· Bus device components & function· Medium
▸
Correct answer
A — It regulates the interaction between sensors and actuators and has no physical inputs or outputs
Learning tip
Correct: The text defines a controller exactly this way.
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Q17
In this KNX chapter, what does the abbreviation 'PEI' stand for?
- A.Programmable Electronic Interface
- B.Physical External Interface
- C.Peripheral Equipment Input
- D.Power Extension Interface
KNX Bus Devices· Bus device components & function· Easy
▸
Correct answer
B — Physical External Interface
Learning tip
Correct: The chapter's abbreviation list defines PEI as Physical External Interface.
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Q18
In start/stop dimming, what does the push button transmit when the rocker is pressed for less than the parameterized time (e.g. < 500 ms)?
- A.A 'start dimming' telegram.
- B.A 'stop dimming' telegram.
- C.A cyclical 'increase brightness by 12.5 %' telegram.
- D.A switching (on/off) telegram.
KNX Bus Devices· Classical application functions: dimming· Medium
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Correct answer
D — A switching (on/off) telegram.
Learning tip
Correct: a press below the parameterized threshold is interpreted as a switch command; only a longer press starts dimming.
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Q19
In start/stop dimming, operating the rocker longer than the parameterized time transmits a 'start dimming' telegram.
TrueFalse
KNX Bus Devices· Classical application functions: dimming· Easy
Correct answer
True
Learning tip
True. A press longer than the parameterized time is interpreted as the beginning of a dimming action ('start dimming').
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Q20
In start/stop dimming, when is the 'stop dimming' telegram sent?
- A.Cyclically, every 12.5 % step.
- B.As soon as the rocker is released.
- C.Automatically once the actuator reaches 100 %.
- D.After a fixed time set in the actuator.
KNX Bus Devices· Classical application functions: dimming· Medium
▸
Correct answer
B — As soon as the rocker is released.
Learning tip
Correct: releasing the rocker generates the single 'stop dimming' telegram.
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Q21
In the KNX dimming application, what is the counterpart to the dimming sensor (push button) function?
- A.The dimming actuator.
- B.The line coupler.
- C.The bus power supply.
- D.A second push button.
KNX Bus Devices· Classical application functions: dimming· Easy
▸
Correct answer
A — The dimming actuator.
Learning tip
Correct: the dimming actuator is the receiving counterpart that controls the lamp/ballast.
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Q22
Which device determines the dimming speed in a KNX dimming application?
- A.The push button sensor that starts dimming.
- B.The dimming actuator, via its parameterized dimming speed.
- C.The bus power supply.
- D.The group address used for the telegram.
KNX Bus Devices· Classical application functions: dimming· Medium
▸
Correct answer
B — The dimming actuator, via its parameterized dimming speed.
Learning tip
Correct: every dimming actuator has a parameterized dimming speed; it is an exclusive matter of the actuator.
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Q23
Blind and shutter control, like dimming, distinguishes between a brief and a long operation of the rocker.
TrueFalse
KNX Bus Devices· Drive control (shutter/blinds)· Easy
Correct answer
True
Learning tip
True. The course states the blind/shutter operation functions similarly to dimming, distinguishing a brief from a long rocker operation.
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Q24
What is T1 in drive control, and when is it typically used?
- A.It is the slats/blinds boundary time, always 500 ms.
- B.It is the blind travel time from top to bottom.
- C.It is the debouncing time for push button interfaces and binary inputs; push buttons normally need none.
- D.It is the actuator's dimming speed.
KNX Bus Devices· Drive control (shutter/blinds)· Medium
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Correct answer
C — It is the debouncing time for push button interfaces and binary inputs; push buttons normally need none.
Learning tip
Correct: T1 debounces contact inputs; genuine push buttons normally require no debouncing time.
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Q25
Which rocker action corresponds to which drive-control command?
- A.Brief operation drives blinds up/down; long operation steps the slats.
- B.Brief operation steps the slats; long operation drives the blinds up/down.
- C.Both brief and long operation drive the blinds up/down.
- D.Both brief and long operation only step the slats.
KNX Bus Devices· Drive control (shutter/blinds)· Medium
▸
Correct answer
B — Brief operation steps the slats; long operation drives the blinds up/down.
Learning tip
Correct: a brief press steps the slats, a long press drives the blind up/down.
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Q26
The mask version stored in a KNX device consists of 4 bytes.
TrueFalse
KNX Bus Devices· Data stored in a device & system profiles· Easy
Correct answer
False
Learning tip
The mask version consists of 2 bytes, not 4.
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Q27
What is the 'device descriptor type 0' of a KNX device?
- A.The KNX serial number assigned in the factory
- B.The individual address of the device
- C.The manufacturer code of the application program
- D.Another name for the mask version, identifying the system-software profile
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
D — Another name for the mask version, identifying the system-software profile
Learning tip
Correct: The system-software profile is identified by a mask version, also called device descriptor type 0.
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Q28
Which of the following is NOT normally stored in the memory of a KNX device?
- A.The ETS project backup file
- B.The system software (system stack / KNX operating system)
- C.The application program, individual and group addresses and parameters
- D.Temporary values of the system (RAM content) and the application
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
A — The ETS project backup file
Learning tip
Correct: the ETS project file is not stored in the device. The device retains its operating and configuration data; a BCU key can also be stored in a compatible device to control access. That key is not a recoverable backup of the ETS project: preserving the project and its key remains essential.
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Q29
What happens to the temporary RAM values of a KNX device when the bus power fails?
- A.They are always retained because RAM is non-volatile
- B.They are lost, unless previously saved in non-volatile memory
- C.They are automatically uploaded to the ETS project
- D.They overwrite the mask version
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
B — They are lost, unless previously saved in non-volatile memory
Learning tip
Correct: RAM (temporary) values are lost on a bus power failure unless the device saved them earlier in non-volatile memory.
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Q30
Under what condition can an application program be downloaded into a BCU?
- A.Any application program can be downloaded into any BCU regardless of manufacturer
- B.Only if the two devices share the same individual address
- C.The manufacturer code of the application program and of the BCU must match
- D.Only if the mask version is set to 0000h first
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
C — The manufacturer code of the application program and of the BCU must match
Learning tip
Correct: The manufacturer code of the program and of the BCU must match to allow the download.
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Q31
How does an E-mode device report which functionality (channels) it supports?
- A.By means of device descriptor 2
- B.By means of device descriptor type 0 (the mask version)
- C.By downloading product data from the KNX Online Catalog
- D.By its KNX serial number
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
A — By means of device descriptor 2
Learning tip
Correct: E-mode devices report their supported functionality via device descriptor 2, a different descriptor than S-mode devices.
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Q32
How are E-mode KNX devices linked and their parameters set?
- A.Only by a full ETS download of the application program
- B.Via appropriate hardware settings or via a central controller
- C.By editing the 2-byte mask version in the device
- D.Automatically, with no configuration of any kind
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
B — Via appropriate hardware settings or via a central controller
Learning tip
Correct: For E-mode devices the linking and parameter setting is ensured via hardware settings or a central controller.
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Q33
When was System 1 technology introduced, and what is its status today?
- A.In 1991, but it has since been removed from the KNX Standard
- B.In the late 1990s, together with System 2 and System 7
- C.With the first generation of KNX devices in 1991; it is still part of the KNX Standard
- D.With ETS6.1.1, as the newest profile
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
C — With the first generation of KNX devices in 1991; it is still part of the KNX Standard
Learning tip
Correct: System 1 came with the first KNX device generation in 1991 and remains part of the KNX Standard.
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Q34
What is the maximum number of group objects for a System 1 device?
- A.254
- B.65536
- C.65535
- D.12
KNX Bus Devices· Data stored in a device & system profiles· Easy
▸
Correct answer
D — 12
Learning tip
Correct: System 1 supports a maximum of 12 group objects.
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Q35
How many group objects can a System 2/7 device support at most?
- A.254
- B.255
- C.12
- D.65536
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
A — 254
Learning tip
Correct: System 2/7 devices support up to 254 group objects.
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Q36
When a tool wants to read or write the memory of a System 2, 7 or B device, how must it authorize itself?
- A.With an authorization key of 2 bytes
- B.With an authorization key of 4 bytes
- C.With an authorization key of 6 bytes
- D.No authorization is needed for System 2, 7 or B devices
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
B — With an authorization key of 4 bytes
Learning tip
Correct: Access requires the tool to first authorize itself with a 4-byte authorization key.
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Q37
From which ETS release is addressing via the KNX serial number supported by default, and what is the alternative before that?
- A.Supported by default from ETS6.1.1; ETS Apps in the MyKNX shop also provide it
- B.Supported by default from ETS4; no apps exist for it
- C.Supported by default from ETS6.1.1; but no other tool can do it
- D.Never supported by ETS; only special hardware can do it
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
A — Supported by default from ETS6.1.1; ETS Apps in the MyKNX shop also provide it
Learning tip
Correct: The feature is supported by default with ETS6.1.1, and MyKNX-shop ETS Apps also allow reading/writing the individual address without the programming button.
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Q38
What can an ETS end user (system integrator) do with interface objects via the ETS 'Device Editor' App?
- A.Both read and freely rewrite them at will
- B.Only read them; manipulating them requires the deeper knowledge taught in the KNX tutor course
- C.Neither read nor write them
- D.Delete them to reset the device
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
B — Only read them; manipulating them requires the deeper knowledge taught in the KNX tutor course
Learning tip
Correct: The system integrator cannot manipulate interface objects but can read them with the Device Editor App; manipulation needs tutor-course knowledge.
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Q39
Why are the maxima of 65536 group objects and 65535 group addresses described as essentially theoretical?
- A.Because no KNX device can physically store more than 254 objects
- B.Because the ETS caps every project at 254 group objects
- C.Because they are normally not reached by current applications
- D.Because the values apply only to System 1 devices
KNX Bus Devices· Data stored in a device & system profiles· Medium
▸
Correct answer
C — Because they are normally not reached by current applications
Learning tip
Correct: The text calls them a pure theoretical value, normally not reached by current applications, comparable to the total address capacity of a KNX system.
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