Every KNX device requires a unique physical address — also called the individual address — in the format area.line.device (e.g. 1.2.15). Physical addresses define the device's location in the KNX topology: area (1-15), line (1-15 per area), device (1-255 per line). The physical address is assigned during device commissioning and stored in the device's non-volatile memory. Without a correctly assigned physical address, ETS6 cannot communicate with the device, cannot program its parameters, and cannot assign group addresses. Understanding the three address assignment methods is essential for any KNX commissioning engineer.

Factory default state

Every KNX device leaves the factory with physical address 15.15.255 (the "programming address"). Multiple new devices on the same bus with address 15.15.255 do not conflict — KNX protocol handles this with the learning mode mechanism. When a device is in programming mode (indicated by a flashing programming LED, usually activated by pressing a programming button), it exclusively responds to programming telegrams from ETS6. Only one device should be in programming mode at a time on a bus segment.

Method 1 — Push-button (most common in practice)

Step 1: In ETS6, open the project and select the device to program (e.g. MDT AKD-0802.01 relay actuator at topology position 1.1.15). Step 2: Connect ETS6 laptop to KNX via USB interface (e.g. Weinzierl USB Interface 5259) or KNXnet/IP (via KNX IP router on LAN). Step 3: In ETS6, click "Download" → select "Individual Address" only. ETS6 sends a broadcast programming address telegram and waits. Step 4: Press the programming button on the physical device (small button usually on front face of DIN-rail module, pressing activates programming LED). Step 5: Device responds to ETS6 "I am here" — ETS6 assigns address 1.1.15 to that device. Programming LED stops flashing, confirms success. Repeat for each device. Time per device: 15-30 seconds.

Method 2 — ETS6 bus scan with automatic discovery

When installing new devices that are still at factory address 15.15.255: use ETS6 Bus Monitor or the "Determine individual address" function to scan the bus. ETS6 sends a scan telegram to address 15.15.255 — all devices in factory state respond. ETS6 shows a list of discovered "unknown" devices. Select each device, enter its desired physical address in ETS6, then press the device's programming button when prompted. ETS6 assigns the address. This method is useful for commissioning many devices in parallel — scan once to see all factory-default devices, then assign sequentially.

Method 3 — ETS6 Download with automatic address detection

For devices already in an ETS6 project (with physical addresses assigned in the project but not yet programmed to hardware): use ETS6 "Download All" with the "Determine device before download" checkbox. ETS6 sends programming address broadcast, waits for user to press programming button on each device in sequence, automatically assigns the correct physical address from the project, then downloads all parameters and group addresses in one step. This is the fastest method when commissioning a complete system for the first time — ETS6 handles both address assignment and full configuration download simultaneously.

Physical address topology rules

Area 1-15, lines 1-15, devices 1-255 per line. Reserved addresses: 0.0.0 = broadcast (never assign to a device). 15.15.255 = factory default (never assign in a real project). Line coupler physical address: always X.Y.0 (device part = 0). Area coupler physical address: always X.0.0. Best practice address structure: Area 1 = main building, Area 2 = annex, Area 3 = garage. Line 1 = ground floor, Line 2 = first floor, Line 3 = second floor, Line 4 = garden. Within each line: devices 1-10 = actuators, 11-30 = sensors/pushbuttons, 31-50 = binary inputs, 51-60 = system devices (PSU, coupler). Document the topology convention in the ETS6 project description and as-built panel documentation — enables any future engineer to understand the addressing scheme without the project file.

Addressing errors and recovery

Duplicate address: two devices with same physical address cause communication errors — both respond simultaneously, corrupting telegrams. ETS6 will report an error during download. Recovery: put one device in programming mode (press button), ETS6 bus scan detects it at the duplicate address — reassign to the correct unique address. Wrong address: device programmed with address from a different project or a different device position — ETS6 download to the wrong device. Recovery: bus scan → identify the incorrectly addressed device by address → reassign. Factory reset: most KNX devices can be reset to 15.15.255 by holding the programming button for 5-10 seconds — consult device manual for exact procedure.