A-LevelComputer ScienceHardware9618/32 · Oct/Nov 2022 · Q88 Marks

Draw a logic circuit for an SR flip-flop and label the inputs. [Figure X.X]

(a)Draw a logic circuit for an SR flip-flop and label the inputs. [Figure X.X][4]
(b)State the purpose of a flip-flop.[1]
(c)Simplify the following expression using Boolean algebra, including De Morgan's laws. Show your working. (A.B).(A.C).(B.D)[3]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] (a) One mark for each point (Max 4) • One correct NAND or NOR gate with two separate inputs and one output
[1] (a) • Second correct logic gate of same type as first with two separate inputs and one output
[1] (a) • Correct connections between logic gates
[1] (a) • Correctly labelled inputs
[1] (b) To store a binary digit / (single) bit.
[1] (c) One mark for each point (Max 3) • Correct application of De Morgan’s Law
[1] (c) • Correct application of Double Negation Law or Distributive Law
[1] (c) • Correct answer (A.B).(A.C).(B.D) = (Ā.B) + (A.C) + (B.D) [1] = (A.B) + (A.C) + (B.D) [1] Ā. (B + C) + B.D [1]

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