A KNX TP line can accommodate up to 256 devices when line repeaters are used.

A KNX TP line natively supports up to 64 devices in a single segment. With line repeaters, the line can be extended to four segments of 64 devices each, giving a maximum of 4 x 64 = 256 devices on one logical line. Each segment still requires its own power supply.

Even with repeaters, every additional segment needs its own power supply — do not forget the PSU when sizing a 256-device line.