Problem
When trying to download a device, the following error message is shown:
This operation requires an APDU length of xx bytes, but only yy is available due to the capabilities of the device.
Where xx and yy are amount of bytes.
Cause
This situation often indicates a discrepancy in the Application Protocol Data Unit (APDU) length capabilities between two communicating KNX devices or between ETS and the target device (i.e., the device being programmed). KNX devices can have different APDU length capacities for standard or extended frames. When ETS attempts to send telegrams with longer APDU lengths (e.g., 23 bytes) to a device that only supports a shorter APDU length (e.g., 15 bytes), or if any of the devices along the download path until the target device (e.g., line couplers, interfaces) only support a shorter APDU length, this error can occur.
Solution
Replace the device with the limited APDU length capabilities with one that supports longer APDU length frames.