Labelling inputs and the output: A, B, C and X

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which letter is used to label the output of a logic circuit in IGCSE questions?

A X

B Z

2. Which set of labels is used for the inputs of a circuit with three inputs?

A A, B and C

B X, Y and Z

3. Where are the inputs drawn in a logic circuit diagram?

A On the left

B On the right

4. Where is the output X drawn in a logic circuit diagram?

A On the left

B On the right

5. How many outputs does an exam logic circuit have?

A Two outputs, X and Y

B One output, X

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1X = A AND B		AThis gives two outputs, X and Y. A circuit has one output only, labelled X.
2X = (A OR B) AND C		BX = NOT A
3The output of a circuit is always labelled X, and it is written on the left of the equals sign		CThe circuit has three inputs A, B and C and one output X
4A circuit with three inputs labels them A, B and C, and they sit on the left of the diagram		DThe inputs are written as lowercase letters. They must be capital letters A and B.
5X = a AND b		EX = (A AND B) OR C
6X = A AND B and Y = A OR B		FA and B are the two inputs and X is the single output of the circuit

Definitions

A, B, C and X

Fill in the Blanks

Complete each line of code by filling in the missing parts.

_ = A AND B

X = (A AND B) OR _

Input 1: A Input 2: _ Input 3: C

Number of outputs: _

Inputs on the left, output on the _____

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Inputs on the left: A, B

B Output on the right: X

C Q = A AND B

Question 2

A INPUT A

B INPUT D

C X = A OR B

Question 3

A INPUT A

B INPUT B

C INPUT C

D Y = (A AND B) OR C

Question 4

A Inputs: A, B, C

B Position: left of circuit

C Output: X

D Position: left of circuit

Question 5

A A, B and C are inputs

B They are drawn on the left

C X and Y are the outputs

Answer Key

Labelling inputs and the output: A, B, C and X

Section A: Quick Questions

A — X

A — A, B and C

A — On the left

B — On the right

B — One output, X

Section B: Match the Pairs

X = A AND B → A and B are the two inputs and X is the single output of the circuit

X = (A OR B) AND C → The circuit has three inputs A, B and C and one output X

The output of a circuit is always labelled X, and it is written on the left of the equals sign → X = NOT A

A circuit with three inputs labels them A, B and C, and they sit on the left of the diagram → X = (A AND B) OR C

X = a AND b → The inputs are written as lowercase letters. They must be capital letters A and B.

X = A AND B and Y = A OR B → This gives two outputs, X and Y. A circuit has one output only, labelled X.

Section C: Definitions

A, B, C and X — In a logic circuit, the inputs are labelled with capital letters A, B and C on the left, and the single output is labelled X on the right.

Section D: Fill in the Blanks

X = A AND B

X = (A AND B) OR C

Input 1: A
Input 2: B
Input 3: C

Number of outputs: 1

Inputs on the left, output on the right

Section E: Spot the Error

C — The output of a logic circuit is always labelled X, so the expression must start with X, not Q. It should be X = A AND B.

B — Inputs are labelled A, B and C. The expression uses B, so the second input must be INPUT B, not D.

D — The single output must be labelled X, not Y. The line should be X = (A AND B) OR C.

D — The output X is drawn on the right of the circuit, not the left. Only the inputs are on the left.

C — A circuit in this course has one output only, labelled X. There is no second output Y.