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Exercise DET-04.05 – Combinational or sequential

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Prof. Dr. Thorsten Jungmann (last updated 2026-10-25)

Relates to DET-04 Algorithmic minimization of functions with many inputs and hazard analysis

Task

The output of a combinational logic circuit depends only on its present inputs; a sequential circuit also depends on past inputs and stores information as its state. For each of the following functions, decide whether a combinational logic circuit suffices or whether a sequential circuit is needed, and give a reason.

a) Five functions of a smartphone, as Apple describes them for the iPhone:

  1. While Low Power Mode is on, the battery icon is yellow.
  2. Low Power Mode turns off when the battery is charged to 80 % or more.
  3. A press of the power button (on an iPhone, the side button) wakes the phone; the next press locks it again.
  4. The phone locks automatically if you don’t touch the screen for a minute or so.
  5. When the setting System Haptics is off, the phone does not vibrate for incoming calls.

b) Five functions of the heat pump of our example system:

  1. Its two switching signals of Smart Grid Ready (SG Ready) select one of four operating states.
  2. During a block by the energy supplier, the heat pump must not start; only frost protection is ensured.
  3. In the comfort time, a hot-water charging starts when the water falls below 47.5 °C, and it runs until the water has reached about 54 °C.
  4. The fault list keeps each fault with its number, the heat pump and the date and time.
  5. The controller counts the defrosting starts of each heat pump: 857 and 843 so far.

c) A short spurious pulse reaches an input of each of these functions. Which of the functions can it change permanently? Explain it with one function from a) and one from b).

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