E-LESSON-3-4

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B.C.A 2 All right are reserved with CU-IDOL Digital Circuits and Logic Designs Course Code: BCA111 Semester: First SLM Units: e-Lesson No: 3-4 2 www.cuidol.in Unit-3, 4 (BCA111)

Logic Gates 33 OBJECTIVES INTRINOTDRUOCDTUIOCNTION Student will be able to understand the basic gates In this session we are going to learn about like AND, OR and NOT gates. • Basic gates like AND, OR and NOT gates. • Working of universal gates Student will be able to describe working of • Conversion of logic gates using universal universal gates gates. Student will be able to do conversion of logic gates using universal gates. www.cuidol.in Unit-3, 4 (BCA111) AINllSTrIiTgUhTtEarOeFrDeIsSeTrAvNeCdEwAitNhDCOUN-ILDINOELLEARNING

TOPICS TO BE COVERED 4 1. Positive and negative logic 2. Basic GATES 3. Universal Gates www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

Positive and negative logic 5 • In a positive logic system, the most positive voltage level (high) represent the logic 1 state. The most negative voltage level (low) represents the logic 0 state. • In a negative logic system , the most positive voltage level (high) represent the logic 0 state. The most negative voltage level (low) represents the logic 1 state. • For example, if the voltage levels are -0.1 V and -5V, then in a positive logic system the -5 V level represents a 0 state and -0.1level represents a 1 state, in then in a negative logic system the -5 V level represents a 1 state and -0.1V level represents a 0 state. • if the voltage levels are 0.1 V and 5V, then in a positive logic system the 5 V level represents a 1 state and 0.1level represents a 0 state, in then in a negative logic system the 5 V level represents a 0 state and 0.1 V level represents a 1 state www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

AND GATE 6 OR GATE www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

The NOT GATE (or inverter) 7 www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

NAND gate 8 NOR gate www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

Exclusive OR gate 9 Exclusive NOR gate www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

NAND AS UNIVERSAL GATE 10 www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

NOR GATE AS UNIVERSAL GATE 11 www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

Multiple Choice Questions 1. __________ gate is also known as “inverter”. 12 (a) Not (b) OR (c) AND (d) NAND 2. Y = A + B is the equation of __________ gate. (a) X-OR (b) OR (c) NOT (d) NOR 3. Y = A is equation of __________ gate. (a) OR (b) NOR (c) NOT (d) AND Answers:1.(a) 2.(b) 3.(c) Unit-3, 4 (BCA111) All right are reserved with CU-IDOL www.cuidol.in

Multiple Choice Questions 13 4. Positive logic inputs and outputs are also called __________. (a) Toggle (b) Active low (c) Zero (d) Active high 5. A __________ is an electronic device which is used to make logical decisions. (a) Logic gate (b) Encoder (c) Decoder (d) Mux Answers:4.(d) 5.(a) www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

SUMMARY Let us recapitulate the important concepts discussed in this session: 14 •Logic Gates used in Digital Computers. Electrical signals such as voltages exist throughout the computer in either one of the two recognizable states. The two states represent a binary variable that can be equal to 1 or 0. •Logic gates are the basic building blocks of any digital system. It is an electronic circuit having one or more than one input and only one output. The relationship between the input and the output is based on a certain logic. Based on this, logic gates are named as AND gate, OR gate, NOT gate etc. An AND gate produces a 1 output when all of its inputs are 1s. •An AND gate performs the basic operation of multiplication. An OR gate produces a 1 output if any of its inputs are 1s. An OR gate performs the basic operation of addition. A NOT gate performs the function called inversion or complementation. A NOT gate converts the input state to an opposite output state. •A NAND gate is a combination of an AND gate and an inverter. A NAND gate produces 1 output when any of the inputs are 0s. A NOR gate is a combination of an OR gate and an inverter. A NOR gate produces a 1 output only when both inputs are 0s. Boolean functions may be practically implemented by using electronic gates. www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

FREQUENTLY ASKED QUESTION Q1. 1. Explain truth table of NOT gates. 15 Ans: The NOT gate is a digital logic gate with one input and one output that operates an inverter operation of the input. The output of the NOT gate is the reverse of the input. When the input of the NOT gate is true then the output will be false and vice versa. The symbol and truth table of a NOT gate with one input is shown in the adjoining figure. For further details refer SLM unit 4 in details. 2. Describe the working of NAND Gate. Ans: The NAND gate is a digital logic gate with ‘n’ i/p and one o/p, that performs the operation of the AND gate followed by the operation of the NOT gate. NAND gate is designed by combining the AND and NOT gates. If the input of the NAND gate high, then the output of the gate will be low. The symbol and truth table of the NAND gate with two inputs is shown in the adjoining figure. For further details refer SLM unit 4 in details. 3. Explain functioning of NOR Gate. Ans: The NOR gate is a digital logic gate with n inputs and one output, that performs the operation of the OR gate followed by the NOT gate. NOR gate is designed by combining the OR and NOT gate. When any one of the i/ps of the NOR gate is true, then the output of the NOR gate will be false. For further details refer SLM unit 4. www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

REFERENCES 16 1. www.tutorialspoint.com 2. Self Learning Material, Institute of Distance and Online Learning, Chandigarh University 3. docplayer.net 4. www.csie.nuk.edu.tw 5. www.thevbprogrammer.com 6. probabilitylectures.narod.ru 7. ergopalkrishnawithc.blogspot.in 8. www.ensolt.com 9. www.encoder.com 10. Lala. \"Number Systems and Binary Codes\", Principles of Modern Digital Design, 11. www.slideshare.net 12. www.freepatentsonline.com www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL

17 THANK YOU www.cuidol.in Unit-3, 4 (BCA111) All right are reserved with CU-IDOL