KNX Group Address

This information is based on version 1.1 of the KNX specification.

KNX Address defined in the Data Link Layer is a two byte field, consisting of address high byte (a.k.a Octet 0) and low byte (a.k.a Octet 1).

The structure and semantics of these two bytes differs depending on whether a group address or individual address is being used.

KNX Group Address

KNX Group addresses are defined as follows:

                 +-----------------------------------------------+
       16 bits   |                 GROUP ADDRESS                 |
                 +-----------------------+-----------------------+
                 | OCTET 0 (high byte)   |  OCTET 1 (low byte)   |
                 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          bits   | 7| 6| 5| 4| 3| 2| 1| 0| 7| 6| 5| 4| 3| 2| 1| 0|
                 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                 |  |  Main Group (S13)  |   Sub Group (S13)     |
                 +--+--------------------+-----------------------+

• KNX group addresses do not need to be unique and a device may have more than one group address.
• Group addresses are defined globally for the entire KNX network (however, in the message frames it is possible to restrict the number of routers that can be crossed to reach devices).
• A group address zero is sent to every device (it is a broadcast).

No further definition of structure Main Group (what appears a 7 bit value) and Sub Group (a 8 bit value) fields are given.

By convention, KNX group addresses are structured with main/middle/sub levels (5/3/8 bits respectively) or main/sub levels (5/11 bits respectively).