Flags - KNX Association

Flags
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Table of Contents
1
Flags ..........................................................................................................................3
1.1
Setting the Flags ................................................................................................3
1.1.1
1.1.2
1.2
The Communication Flag ‘C’ ..............................................................................4
1.2.1
1.3
Example of a Read Flag .................................................................................6
The Write Flag ‘W’ .............................................................................................8
The Transmit Flag ‘T’ .........................................................................................8
1.5.1
1.6
1.7
Example of a Communication Flag .................................................................5
The Read Flag ‘R’ ..............................................................................................5
1.3.1
1.4
1.5
Example: Setting a Flag in Buildings/Functions View......................................3
Example: Setting Several Flags ......................................................................4
Example of a Transmit Flag ............................................................................9
The Update Flag ‘U’ ...........................................................................................9
The Read on Init Flag .......................................................................................10
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1 Flags
Each group object has 6 flags. These flags control the communication possibilities of an
object on the bus.
Figure 1: Flags
1.1 Setting the Flags
The setting of the flags can take place in Buildings/Functions view, Group Addresses view
and in the Topology view at the objects of the devices. The flags can be set individually or
in groups.
1.1.1 Example: Setting a Flag in Buildings/Functions View
Figure 2: Setting a flag in Buildings/Functions view
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1.1.2 Example: Setting Several Flags
Figure 3: Setting several flags
1.2 The Communication Flag ‘C’
Figure 4: Communication flag "C"
The communication flag is the “master switch” for communication i.e. if this flag is not
set, the object cannot send or receive telegrams. The communication flag is set for all
objects by default. It may be necessary to delete the communication flag in certain
configurations e.g. when objects are not used. If this is the case, it is highlighted in the
application descriptions of the manufacturer. If this object is linked to a group, an
acknowledgement is sent even though the communication flag has been deleted.
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1.2.1 Example of a Communication Flag
In the case of the objects of the light mood push button depicted in the following diagram,
the communication flag must be removed for unused objects.
Figure 5: Removal of communication flag for unused objects
1.3 The Read Flag ‘R’
The read flag enables the object value to be read out i.e. a response telegram is only sent
after a read telegram if the read flag of the object has been set. This function is required
for visualisation, light scenes etc. to query the current object status. The read flag is not
set by default in most cases. The flag is set by many manufacturers for status objects.
Figure 6: The Read flag "R"
Some specific features should be noted when using read flags:
If read flags are used in an installation (e.g. when storing light scenes), it should be
ensured that the read flag is only set once for each group address in order to avoid
multiple responses after a read request.
The read flag should only be set at the bus device which is to respond.
The group address that is used to read out the object status must be placed at the
transmission point of the bus device that should be read out since the response
telegram uses this group address.
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Example: Group for read request is 4/0/12
Incorrect:
Figure 7: Incorrect: Group for read request is 4/0/12
Correct:
Figure 8: Correct: Group for read request is 4/0/12
1.3.1 Example of a Read Flag
In the following example, a read request is sent by a lightscene module. The actuator
reacts with a response telegram. The group address of the central function “All lighting
ON/OFF” is however present at the transmission point. As a result, the lighting throughout
the building is switched on or off by the response telegram, depending on the status of
the queried actuator.
Figure 9: Example: read request sent by a lightscene module
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Figure 10: Group content: Lounge lighting
Figure 11: Group content: Staircase lighting
Figure 12: Group content: All lighting ON/OFF
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1.4 The Write Flag ‘W’
The write flag enables the object status to be modified via the bus on the basis of a
telegram. (The object status can be overwritten). This means that an actuator can only
switch if the write flag has been set for the switch object.
The write flag is set by default for all switch objects, value objects (actuator) as well as all
push button objects (e.g. due to the update for TOGGLE functions).
Figure 13: The Write Flag "W"
1.5 The Transmit Flag ‘T’
The transmit flag enables the group object to send telegrams (transmit telegrams on the
bus). The sending of telegrams can be triggered e.g. by a push button action, a variation
in the temperature or a change in the object status. The telegram can however also be
triggered by the application program.
The transmit flag is dependent on the application and set for sensors by default. In the
case of status objects of actuators, the transmit flag is also mainly set as standard.
Figure 14: The Transmit Flag "T"
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1.5.1 Example of a Transmit Flag
Figure 15: Example of a Transmit Flag
Two dimming actuators should be switched in parallel. In the following example, the
transmit flag has been set for both dimming actuators. As a result, the bus is put under a
heavy load by the respective response telegrams and the dimmers no longer react.
1.6 The Update Flag
If the update flag is set, a response telegram of a read procedure is interpreted as a write
telegram i.e. the object status of the bus device is changed. The selection and evaluation
of the update flag can only be carried out by BCU 2 bus couplers and BIM 112.
BCU 1 bus couplers always interpret response telegrams as write telegrams and
therefore modify their object status.
Figure 16: The Update Flag
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1.7 The Read on Init Flag
If the Read on Init flag is set, the bus device will independently read the value of its
sending group address at initialisation.
The Read on Init flag can at the moment only be set on System B devices (Mask version
$07B0 and $17B0).
Figure 17: The Read on Init Flag
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