This key facts covers Reading Boolean Expressions from Circuit Diagrams within Boolean Expressions for GCSE Computer Science. Revise Boolean Expressions in 3.4 Computer Systems for GCSE Computer Science with 17 exam-style questions and 22 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 6 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Reading Boolean Expressions from Circuit Diagrams
Work LEFT to RIGHT through the circuit, writing down what each gate does:
| Circuit Description | Step-by-Step Build-Up | Final Boolean Expression |
|---|---|---|
| A and B go into AND gate | A → AND ← B | A AND B |
| A goes through NOT gate, output goes to AND with B | A → NOT → AND ← B | NOT(A) AND B |
| A and B into OR gate, result goes into NOT gate | A → OR ← B → NOT | NOT(A OR B) |
| A and B into AND gate, result goes to OR gate along with C | A → AND ← B → OR ← C | (A AND B) OR C |
| A through NOT, B as-is, both to OR, then to AND with C | NOT(A) → OR ← B → AND ← C | (NOT(A) OR B) AND C |
Pro tip: Always add brackets to make the order clear, especially with mixed operations!
Practice questions for Boolean Expressions
Which Boolean operator produces an output of 1 only when BOTH inputs are 1?
State De Morgan's first law and give an example to illustrate it.