ITPEC FE Morning October 2018 Question 22

Logic Gates (XOR + AND) — determine output values of a two-stage logic circuit.

Given: A = 1, B = 0, C = 1

Stage 1 — XOR gate (A, B):
- 1 ⊕ 0 = 1
- E = 1

Stage 2 — AND gate (E, C):
- 1 AND 1 = 1
- Y = 1

Why not others:
- (a) E = 0, Y = 0 — XOR(1, 0) = 1, so E is not 0
- (b) E = 0, Y = 1 — same, E is not 0
- (c) E = 1, Y = 0 — AND(1, 1) = 1, so Y is not 0

Key rule: Read the circuit carefully — count how many inputs each gate has. XOR(A, B) has two inputs; C is routed separately as the second input to the AND gate.

AI-generated — may contain errors