Page 32 - Computer_Science_F5

Note: Using DeMorgan’s theorem, you can create other gates from basic gates. For
example, the NAND gate is the same as the OR gate with inverted inputs as
shown in Figure 1.16. Chapter One: Computer architecture

A
FOR ONLINE READING ONLY
Y A
B Y
B

(a) (b)
Figure 1.16: (a) NAND gate, and (b) OR gate with inverted inputs

(5) NOR gate
The term NOR stands for NOT-OR, which refers to the complement of OR gate
output. It works oppositely to the OR gate. The NOR gate has two or more input
signals, and its output signal complements the OR gate. The logical symbol of the
NOR gate is shown in Figure 1.17 (a). Figure 1.17 (b) illustrates the NOR gate’s
truth table which shows that the output will be 0 when any inputs are 1. When both
inputs are 0, the output will be 1.

OR NOT A B
A Y = A+ B
B Y 0 0 1
0 1 0

A 1 0 0
B Y 1 1 0

(a) (b)
Figure 1.17: NOR gate and truth table for NOR gate
The logical symbol of the exclusive OR (XOR) gate is shown in Figure 1.18 (a).
The XOR has only two inputs, and its output is one (1) only when two inputs are at
opposite inputs, that is, 1 and 0. Figure 1.18 (b) illustrates the XOR gate’s truth table.

A B Y

0 0 0
A 0 1 1
B Y 1 0 1

1 1 0
(a) (b)

Figure 1.18: XOR gate and truth table for XOR gate

23
Student’s Book Form Five

Computer Science Form 5.indd 23 23/07/2024 12:32