AND, OR, NOT, XOR — drawing circuits, completing truth tables, solving logic problems. Jun 2022 Q4(e) and Jun 2023 Q4(e) tested truth tables.
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Craig 'n' Dave · Edexcel 1CP2Logic Gates
Key facts
Gate symbols and truth tables
AND gate — output is 1 only if ALL inputs are 1. Symbol: flat back, curved front.
OR gate — output is 1 if ANY input is 1. Symbol: curved back and front (shield shape).
NOT gate — inverts the input. Output is opposite of input. Symbol: triangle with small circle at output.
XOR gate — output is 1 if inputs are DIFFERENT. Output is 0 if inputs are the same. Symbol: OR gate with extra curved line at input.
NAND = NOT AND. NOR = NOT OR.
Common exam question types
1. Complete a truth table for a given circuit
2. Draw a logic circuit for a Boolean expression
3. Work out the output of a circuit from given inputs
4. Write the Boolean expression for a circuit
AND truth table: 0,0→0 | 0,1→0 | 1,0→0 | 1,1→1
OR truth table: 0,0→0 | 0,1→1 | 1,0→1 | 1,1→1
XOR truth table: 0,0→0 | 0,1→1 | 1,0→1 | 1,1→0
Truth table worked example (Jun 2023 Q4(e))
For two inputs S and M connected by AND gate:
S=0, M=0 → AND output = 0
S=0, M=1 → AND output = 0
S=1, M=0 → AND output = 0
S=1, M=1 → AND output = 1
Four rows are always needed for a 2-input gate (2² = 4 combinations)
Exam questions — 4 questions · 12 marks · from real 1CP2 past papers
1 markAND gate1CP2 style
What is the output of an AND gate when input A = 1 and input B = 0?
A 1
B 0
C It depends on the circuit
D Undefined
1 markXOR gate1CP2 style
What is the output of an XOR gate when both inputs are 1?
A 1 — because at least one input is 1
B 0 — because XOR outputs 1 only when inputs are different
C 1 — because all inputs are 1
D Depends on which input arrived first
4 marksComplete a truth table1CP2 Jun 2023 Q4(e) style
Complete the truth table for a circuit with two inputs (A and B) where the output is: NOT(A) AND B.
For all four combinations of A and B, calculate the output. Show your working. (4 marks)
Hint: Work out NOT(A) first for each row, then AND that result with B. Four rows: (0,0), (0,1), (1,0), (1,1).
+40 XP
2 marksBoolean expression to circuit1CP2 style
Describe (as a list of components and connections) a logic circuit that implements: output = A OR (NOT B). (2 marks)
Hint: Break the expression apart: you need a NOT gate (for B) and an OR gate (combining A and NOT B). Describe the connections.