1. CHAPTER 2
LOGIC GATES

2. BASIC LOGIC GATES 7 types of Logic Gates:
Logic gates are the basic building blocks to form digital circuit.
It has 1 o/p terminal.
O/p either HIGH
(logic 1) or LOW (logic 0) depend on digital level at i/p.
7 types of Logic Gates:
INVERTER
AND OR
NAND
NOR
Exclusive – OR
Exclusive - NOR
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Chapter 2: Logic Gates

3. 2.1.1 NOT / INVERTER Used to complement a digital signal.
It has only 1 output.
INPUT
OUTPUT A X 1
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Chapter 2: Logic Gates

4. 2.1.2 AND GATE It has 2 or more input.
2n possible input combinations, where n = no. of bit.
Operation for AND gates is multiplication (x ).
O/p is HIGH when both input (A and B) are HIGH.
INPUT
OUTPUT
A B X 1
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Chapter 2: Logic Gates

5. TIMING DIAGRAM Draw the waveform of X where X = A.B ECE351
Chapter 2: Logic Gates

6. 2.1.3 OR GATE It has 2 or more input.
2n possible input combinations, where n is no. of bit.
Operation for OR gates is adding (+).
O/p is HIGH whenever input A and B are HIGH or both i/p are HIGH.
INPUT
OUTPUT
A B X 1
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Chapter 2: Logic Gates

7. 2.1.4 NAND GATE The operation is SAME as AND gate.
The o/p of NAND gate is inverted from o/p of AND gate.
Denotes inversion
INPUT
Output
AND
NAND
A B X 1
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Chapter 2: Logic Gates

8. 2.1.5 NOR GATE The operation is the SAME as OR gate.
The o/p NOR gate is inverted from OR gate.
INPUT
OUTPUT
A B X 1
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Chapter 2: Logic Gates

9. 2.1.6 EXCLUSIVE – OR GATE INPUT OUTPUT A B X 0 0 0 1 1 1 0 1 1 ECE351 1
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Chapter 2: Logic Gates

10. 2.1.7 EXCLUSIVE-NOR GATE INPUT OUTPUT A B X 0 0 1 0 1 1 0 1 1 ECE351 1
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Chapter 2: Logic Gates

11. SUMMARY of LOGIC GATES
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Chapter 2: Logic Gates

12. 2.2 IC GATES
Digital logic gate circuits are manufactured as integrated circuits.
A number of gates is enclosed in a single package called Dual Inline Package (DIP) housing for plug in or feedthrough mounting, or Small Outline Integrated Circuit (SOIC) for surface mounting.
Part numbers specify what type of gates are enclosed.
These part numbers are industry standards, meaning that a "74LS02" manufactured by Motorola will be identical in function to a "74LS02" manufactured by Fairchild or by any other manufacturer.
Logic circuit part numbers beginning with "74" are commercial-grade TTL. If the part number begins with the number "54", the chip is a military-grade unit: having a greater operating temperature range, and typically more robust in regard to allowable power supply and signal voltage levels.
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13. Packaging - DIP
Packaging - SOIC
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14. Common TTL "DIP" circuit packages
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15. Universality of NAND & NOR Gates
NAND & NOR gates can be used as:
Inverter gates
AND gates
OR gates
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Chapter 2: Logic Gates

16. Universality of NAND
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17. Universality of NOR
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Chapter 2: Logic Gates

18. Exercise
1.Draw the output waveform C and D, given the input waveforms A and B as shown below.
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Chapter 2: Logic Gates

19. Exercise (cont’d)
2. Refer to the circuit and complete the truth table given. A B C Z 1
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Chapter 2: Logic Gates