KNX Guide: Mastering 'useful data' in the KNX system

Useful data is the communication language of the KNX system, it is called Datapoint Type. KNX control data types define how input objects command output objects to perform specific tasks such as: switching, dimming, up/down, ...

The KNX datapoint type is the standardised control data in every KNX system.

In fact, each Group Object (also called Communication Object) is a 'data point' , representing control data in the KNX system. The KNX standard specifies specific control data types in each case such as: switch / boolean / enable / dimming / step / temperature ...

Let's consider the following example to understand more about 'datapoint type' :

Suppose that a telegram is sent from a sensor to an actuator to turn on a light somewhere in the building. Then, this telegram needs to include two elements:

• 'destination address' = 'destination address' - specifies the location where the light needs to be 'turned on'

• 'switch on' = 'turn on the light' - defines the action the actuator should perform

In fact, this 'switch on' instruction is represented by a 1-bit data and that is the 'datapoint type'. Similarly, the 'dimming brighter' instruction will be represented by a 4-bit data.

The above example shows that, in order to synchronize control functions in the KNX system, it is very important to specify the control data type. It helps KNX devices understand each other (regardless of which manufacturer they are manufactured by) and meet exactly what the design engineer wants.

Group Object Configuration As explained above, each Group Object is, in fact, a Datapoint Type, and therefore, the information of this Datapoint Type:

• is not stored in device memory / is not stored in device memory

• is never included in a telegram

• is only stored in the ETS project / is only stored in the ETS project

Control Datapoint Types are particularly important for diagnostics, for example allowing ETS to interpret data associated with a Group Object, e.g. instead of 'data = 85 A8' 'data = -6 °C' is displayed. Structure and Format Structure of Data Structure:

• data type: format + encoding

• size: value range + unit

Format: X.YYY

• X: defines format + encoding

• YYY: defines value range + unit

The example below will describe more specifically the structure and format of Datapoint Type:

DPT_ID	DPT_Name	Data format	Data type (encoding)	Value range
1.001	DPT_Switch	Switch	1 bit	0=off, 1=on
1.007	DPT_Step	Step	1 bit	0=decrease, stop 1=increase,stop
3.007	DPT_Control_Dimming	Dimming	4 bit	bit 3: 0 = darker bit 3: 1 = brighter bit 0-2: = number of dimming steps

Group Object and Datapoint Type in ETS 6 software.

Common Datapoint Types:

• 1.yyy = boolean, like switching, move up/down, step

• 2.yyy = 2 x boolean, e.g. switching + priority control

• 3.yyy = boolean + 3-bit unsigned value, e.g. dimming up/down

• 4.yyy = character (8-bit)

• 5.yyy = 8-bit unsigned value, like dim value (0..100%), blinds position (0..100%)

• 6.yyy = 8-bit 2's complement, e.g. %

• 7.yyy = 2 x 8-bit unsigned value, i.e. pulse counter

• 8.yyy = 2 x 8-bit 2's complement, e.g. %

• 9.yyy = 16-bit float, e.g. temperature

• 10.yyy = time

• 11.yyy = date

• 12.yyy = 4 x 8-bit unsigned value, i.e. pulse counter

• 13.yyy = 4 x 8-bit 2's complement, i.e. pulse counter

• 14.yyy = 32-bit float, e.g. temperature

• 15.yyy = access control

• 16.yyy = string -> 14 characters (14 x 8-bit)

• 17.yyy = scene number

• 18.yyy = scene control

• 19.yyy = time + data

• 20.yyy = 8-bit enumeration, e.g. HVAC mode ('auto', 'comfort', 'standby', 'economy', 'protection')

Conclusion

KNX Datapoint Type reflects the core of the KNX standard and is important knowledge when designing and programming KNX smart home controls. If you are a KNX programming engineer, you need to master Datapoint Type along with other knowledge such as Topology, Address ...

Source: support.knx.org