Name
Date
LOGIC GATE TRUTH TABLES
The decision makers in electronic systems are called logic gates. They are called gates because
they have to receive the right input signals before they let output information through.
There are 3 sorts of logic gate, their names give you a clue to which input signals are required
before a 1 (high) signal is passed to the output.
Truth tables are used to summarise what output is passed for different combinations of output.
NOT gates
A NOT gate has one input and one output. When the input is 1 (high) its output is 0(low). When
the input is 0 the output is 1. In other words when the input is 1 its output is NOT 1.
A
Q
1
0
Fill in the table.
NOW COMPLETE THE TRUTH TABLES FOR THE OTHER GATES. YOU CAN USE
THE DECISION BOARDS TO HELP YOU COMPLETE THE TABLES.
AND gates
An AND gate has two inputs (on the left) and one output (on the right). The output is 1 (high)
only when input A and input B are ___ (__________).
A
B
Q
1
1
0
OR gates
An OR gate has two inputs (on the left) and one output (on the right). The output is 1 (high)
when either input A or input B (or both) are ___ (__________).
A
B
Q
1
1
0