DESCRIPTION OF ALTERNATIVE LOGIC GATE

 

 

WEEK: 6

CLASS: SS 2

SUBJECT: COMPUTER SCIENCE

 

TOPIC: LOGIC CIRCUIT (II)

CONTENT: Alternative logic gates:

• Description of alternative logic gate
• Types of alternative logic gates NAND, NOR
• Symbols of each logic gate
• Input/output signals for: NAND, NOR

 

Sub-Topic 1: DESCRIPTION OF ALTERNATIVE LOGIC GATE

Although OR, AND, and NOT gate combinations are good enough for the construction of any logic operation, there are alternative methods that could be used. The alternative logic gates are NAND and the NOR logic gates. Alternative methods using NAND and NOR gates are more economical and therefore more widely used.

All logic operations can be performed with combinations of just NANDs or NORs, but a combination of NORs with NANDs is usually preferable to one provided just by NANDs.

 

TYPES OF ALTERNATIVE LOGIC GATES

Basic digital logic gates perform logical operations using the following standard single logic gates:

1. Logic “NAND” gate
2. Logic “NOR” gate

 

THE LOGIC “NAND” GATE

 

The logic NAND gate is a combination of the digital logic AND gate with that of an inverter, or NOT gate connected together in series. The NAND (Not AND) gate has an output that is normally at logic level “1” and only goes “LOW” to logic level “0” when ALL of its inputs are at logic level “1”. It is the reverse of the ‘complementary’ form of AND gate.

The Boolean expression for a logic NAND gate, is denoted by a single dot or full stop symbol (.) with a line or overline (-) over the expression to signify the NOT or logical negation of the NAND gate, giving us the Boolean expression of A.B=Q.

 

Sub-Topic 2 : SYMBOLS OF NAND LOGIC GATE

 

 

Inputs                                               Output

 

Shows invasion

 

Inputs                                                                                                      Output

 

 

 

THE LOGIC “NOR” GATE

 

The logic NOR or inclusive NOR gate is a combination of the digital logic OR gate with that of an inverter or NOT gate connected together in series. The NOT (Not OR) gate has an output that is normally at logic “1” and only goes “LOW” to level of “0” when ANY of its inputs are at logic level “1”. The logic NOR gate is the reverse or “complementary” from of the OR gate.

The Boolean expression for a logic NOR gate is denoted by a plus sign (+) with a line or overline (-) over the expression to signify the NOT or logical negation of NOT gate giving us the Boolean expression of A+B=Q

 

 

 

 

 

 

Symbol of NOR Logic gate

 

A.

INPUTS                                                                                                              OUTPUT

Shows inversion

 

 

 

B.

 

INPUTS                                                                                              OUTPUT

 

EVALUATION

 

1. Mention the two main types of alternative logic
2. Show the arithmetic operations of NAND and NOR

 

 

 

READING ASSIGNMENT

Read construction of truth table for NAND and NOR gate, also uses of logic gates and summarize in not more than one page.

 

WEEKEND ASSIGNMENT

Objectives

1. The output of gate negates the output of OR gate.
2.  gate has a ‘D’ shape.
3. The combination of and                          gates is more economical for constructing comparators.
4. The shape of gate is triangle.
5. The symbols that negate the output of a gate are and                    

ESSAY QUESTIONS

1. Construct a truth table of NAND for two
2. List three uses of logic

 

 

QUIZ QUESTIONS

[HDquiz quiz = “824”]