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CHAPTER 2 LOGIC GATES

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**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 ECE351 Chapter 2: Logic Gates

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**2.1.1 NOT / INVERTER Used to complement a digital signal.**

It has only 1 output. INPUT OUTPUT A X 1 ECE351 Chapter 2: Logic Gates

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**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 ECE351 Chapter 2: Logic Gates

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**TIMING DIAGRAM Draw the waveform of X where X = A.B ECE351**

Chapter 2: Logic Gates

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**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 ECE351 Chapter 2: Logic Gates

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**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 ECE351 Chapter 2: Logic Gates

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**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 ECE351 Chapter 2: Logic Gates

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**2.1.6 EXCLUSIVE – OR GATE INPUT OUTPUT A B X 0 0 0 1 1 1 0 1 1 ECE351**

1 ECE351 Chapter 2: Logic Gates

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**2.1.7 EXCLUSIVE-NOR GATE INPUT OUTPUT A B X 0 0 1 0 1 1 0 1 1 ECE351**

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SUMMARY of LOGIC GATES ECE351 Chapter 2: Logic Gates

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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. ECE351 Chapter 2: Logic Gates

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Packaging - DIP Packaging - SOIC ECE351 Chapter 2: Logic Gates

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**Common TTL "DIP" circuit packages**

ECE351 Chapter 2: Logic Gates

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**Universality of NAND & NOR Gates**

NAND & NOR gates can be used as: Inverter gates AND gates OR gates ECE351 Chapter 2: Logic Gates

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Universality of NAND ECE351 Chapter 2: Logic Gates

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Universality of NOR ECE351 Chapter 2: Logic Gates

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Exercise 1.Draw the output waveform C and D, given the input waveforms A and B as shown below. ECE351 Chapter 2: Logic Gates

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Exercise (cont’d) 2. Refer to the circuit and complete the truth table given. A B C Z 1 ECE351 Chapter 2: Logic Gates

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