A-LevelComputer ScienceHardware9618/31 · May/June 2021 · Q78 Marks
The diagram shows a logic circuit. [Figure X.X]
- (a)Complete the truth table for the given logic circuit. Show your working. Inputs A B C 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 Working space P Q R Outputs Y Z[3]
- (b)State the name of the logic circuit.[1]
- (c)Write the Boolean expressions for the two outputs Y and Z in the truth table as sum-of-products and state the purpose of each output. Y = Purpose Z = Purpose[4]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- [1] (a) Working (all three columns P, Q and R correct)
- [1] (a) Correct column Y
- [1] (a) Correct column Z
- [1] (b) Full adder
- [1] (c) Y = A'B'C + A'BC' + AB'C' + ABC (or equivalent minimized)
- [1] (c) Purpose Y: Sum bit
- [1] (c) Z = A'BC + AB'C + ABC' + ABC (or equivalent minimized)
- [1] (c) Purpose Z: Carry output
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