Turn a rule into a logic expression

4 minAS Level3.2.6

By the end of this lesson

By the end you can turn a sentence about when an output should be 1 into a logic expression.

Give each condition a signal name

For a simple example, let A and B name yes/no inputs and Y name the output. If Y is on only when both inputs are true, write Y = A AND B.

First choose a capital letter for each yes/no condition. Here, 1 means that condition is true.

Definition

Logic expression

A logic expression combines input variables using operations such as NOT, AND, OR and XOR to state when an output is 1.

Use brackets to make the intended order unmistakable. Read the expression in words before drawing gates.

Worked example: The powered alarm

The alarm sounds if the door is open OR the manual button is pressed, but only when system power is on.

Have a go first?

Translate the sentence

Fill in the blanksQuestion 1 · Apply

For the example, complete: Alarm = AND ( OR ).

Multiple choiceQuestion 2 · Recall

A lamp is on only if switches A and B are both on. Which expression matches?

AA AND BBA OR BCA XOR BDNOT A AND B

Answer the 2 questions above to continue.