Read a circuit into a truth table

5 minAS Level3.2.5

By the end of this lesson

By the end you can construct a truth table from a problem rule, a circuit or a logic expression.

Same four rows, one gate at a time

With two inputs A and B, start with all four rows: 00, 01, 10, 11. Work from the circuit's input side towards its output.

Let Y name the circuit's final output.

For row 01, NOT A is 1 and B is 1, so (NOT A) AND B gives 1.

If one gate feeds another, make a working column for the first gate. This stops the middle result getting lost.

The circuit computes Y = (NOT A) AND B.

Worked example: Calculate each output row

Construct the truth table for Y = (NOT A) AND B.

Have a go first?

Output row by row

Fill in the blanksQuestion 1 · Stretch

Multiple choiceQuestion 2 · Apply

Answer the 2 questions above to continue.