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Electronics

Combinational logic

  • 5 things to know
  • Paper 3, section B

Overview

The gates and their truth tables, and building larger functions from NAND or NOR.

What you need to know

Answer each one before you reveal it.

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Numbers

How does a NAND gate relate to an AND gate, and what rule defines an OR gate?

Numbers

How many rows of an OR truth table give 1, and when does a NOR gate output 1?

Numbers

What is a truth table, and how are gates combined into larger functions?

Numbers

When constructing a logic circuit from a truth table, which rows of the truth table are relevant?

Key term

Which single gate type, other than NOR, is functionally complete?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How is the Boolean expression for NOT A written?

    Model answer

    A̅ (A with an overline or bar above it)

  2. 2

    What notation is used to represent A AND B in Boolean algebra?

    Model answer

    A·B (A dot B)

  3. 3

    How is the Boolean expression for A OR B written?

    Model answer

    A+B

  4. 4

    Under what input condition does an AND gate produce an output of 1?

    Model answer

    Only when all inputs are 1

  5. 5

    What is the only input condition that causes a NAND gate to output 0?

    Model answer

    When all inputs are 1

  6. 6

    How is the output of a NAND gate related to that of an AND gate?

    Model answer

    The NAND output is the logical inverse (complement) of the AND output

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