Page 45 - Basics of Electrical, Electronic and Communication

244 Chapter 13. Digital Systems

Inputs Output
A B Q = A⊕ B
0 0 1
0 1 0
1 0 0
1 1 1

Table 13.9: Truth table for EX-NOR gate

13.1.4 Universal gates

It is possible to implement any Boolean expression using only NAND
gates. In a similar manner, it can be shown that NOR gates alone can
be used to implement any Boolean operation. Therefore NAND and
NOR gates are called universal gates.
Figure 13.12 illustrates that NOT, AND and OR gates can be im-
plemented using NAND gates.
Figure 13.12 illustrates that NOT, OR and AND gates can also be
implemented using NOR gates.

A A
A.A = A A

A A
A.B = AB A.B
B B

A
A
A.B =A+B A+B
B B

Figure 13.12: NAND as universal gate

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