TP Topology KNX Basic: exam questions with worked answers

Questions for the "TP Topology" topic

1. Q01

   On how many bits is the Group Address encoded inside a KNX TP1 telegram?

   • A.8 bits
   • B.16 bits
   • C.24 bits
   • D.32 bits

   2. TP Topology· Kodierung der Gruppenadresse· Hard

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   Correct answer

   B — 16 bits

   Learning tip

   The Group Address is encoded on 16 bits in the TP1 telegram, regardless of the display structure chosen in ETS (Free, 2-level, 3-level). The display structures merely split the same 16 bits differently for human readability: Free uses 16 free bits, 2-level uses Main (5 bits) / Sub (11 bits), 3-level uses Main (5 bits) / Middle (3 bits) / Sub (8 bits). The wire-level telegram is identical in every case. A and C are wrong because 8 bits would be far too few and 24 bits do not appear in the TP1 frame. D is wrong because 32 bits is the Individual+Group total in some Extended-frame variants, not the Group Address alone.

   Source: KNX Specifications V3.0.0 (public) — Telegram Format, Group Address field

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2. Q02

   The Group Address space in KNX TP1 allows up to 65 536 different Group Addresses (2^16).

   TrueFalse

   2. TP Topology· Adressraum Gruppenadressen· Hard

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   Correct answer

   True

   Learning tip

   A Group Address is encoded on 16 bits inside the telegram, giving 65 536 possible values. In practice, the address 0/0/0 is reserved as a broadcast, so 65 535 addresses remain available for application use. Whether the project uses the 2-level (main/sub) or 3-level (main/middle/sub) representation does not change the underlying 16-bit address space — it only changes how the bits are visually grouped in ETS.

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3. Q03

   Within a KNX area, the maximum number of Line Couplers is 15, one per subsidiary line.

   TrueFalse

   2. TP Topology· Bereichsbegrenzungen· Medium

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   Correct answer

   True

   Learning tip

   True. A KNX area is built around one main line that connects up to 15 subsidiary lines, each attached to the main line through its own Line Coupler. The limit of 15 follows directly from the topology addressing scheme, which reserves 4 bits for the line identifier within an area. Each subsidiary line itself can then host up to 64 devices (or 256 with additional line segments and segment repeaters).

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4. Q04

   In an installation predating 2018, a maximum of 64 sensors, actuators, line couplers and backbone couplers can be connected to a TP main line.

   TrueFalse

   2. TP Topology· Offizielle Musterprüfung 4· Hard

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   Correct answer

   True

   Learning tip

   True. Before the 2018 update of the KNX TP specification, a main line was limited to a single segment of 64 devices (sensors, actuators, line couplers and backbone couplers combined), with no possibility to extend it via repeaters as a regular line could. After 2018, this restriction was lifted and the modern rule allows up to 256 devices in total per main line, in line with the rest of the topology. Legacy installations therefore still operate under the older 64-device cap.

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