Topic 2 Subtopic 5 Universal Gates

Universal gates are the gates that can be used for implementing any gate like AND, OR and NOT, or any combination of these basic gates; NAND and NOR gates. NAND and NOR gates is said to be universal gates because any digital system can be implemented using only one of these gates. Digital circuits are frequently constructed with only NAND or NOR gates; because these gates are easier to fabricate with electronic components. Because of the importance of NAND and NOR in the design of digital circuits, rules and procedures have been developed for the conversion from Boolean functions in terms of AND, OR and NOT into equivalent NAND or NOR logic diagrams. NAND and NOR are called universal gates because any digital system or Boolean function can be implemented with only these gates. 

From DeMorgan theorem, we can see other representation for NAND and NOR gates as follows:

NAND gate (NAND = Not AND)

This is an AND gate with the output inverted, as shown by the 'o' on the output.
The output is true if input A AND input B are NOT both true: Q = NOT (A AND B)
A NAND gate can have two or more inputs, its output is true if NOT all inputs are true.

		Input A Input B Output Q 0 0 1 0 1 1 1 0 1 1 1 0
Traditional symbol	IEC symbol	Truth Table

NOR gate (NOR = Not OR)

This is an OR gate with the output inverted, as shown by the 'o' on the output.
The output Q is true if NOT inputs A OR B are true: Q = NOT (A OR B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.

		Input A Input B Output Q 0 0 1 0 1 0 1 0 0 1 1 0
Traditional symbol	IEC symbol	Truth Table

Tong Weng Seng         B031210084