# Digital Logic (DL) Important Questions

__Binary systems__

- Differentiate between Analog and Digital system. What are the advantages of a digital system?
- What is a digital computer? Explain the working principle of digital computers with a block diagram.
- What do you mean by the Gray code? What are its application?
- What is decimal code? Differentiate between BCD and excess-3 code.
- Explain the error detection code with an example.
- Convert the following decimal numbers to the indicated bases.
- 7562.45 to octal
- 1938.257 to hexadecimal
- 175.175 to binary

- Convert the following hexadecimal number to decimal and octal numbers
- 0FFF
- 3FFF

- Subtract (1010100 – 1000100) using 1’s complement.
- Using 2’s complement, subtract (1000100-1010100).

__Boolean Algebra and Logic Gates__

- State and prove commutative laws, associative laws and distributive law using logic gate and truth table.
- What do you mean by Universal gate? Show that both NAND gate and NOR gate are universal gates.
- State and prove De-Morgan’s theorem 1st and 2nd with logic gates and truth table.
- Explain the duality theorem with example.Simplify the following Boolean functions to a minimum number of literals: xy + x′z + yz
- Prove the Boolean expression: AB + AB′C + A′BC = AB + AC + BC
- What is a logic gate? What are the types of basic gate.
- Draw a logic gates that implement the following:

F = AB + C D' + B' C F = (A + B) (B' + C) (C' + D + E)

- Define integrated circuit. What are the characteristics that describe the performance of IC digital logic families?

__Simplification of Boolean Functions__

__Explain the K-map with three variables. Reduce the following function using k-map__

F = B'D + A'BC' + AB'C + ABC'

- What do you mean by K-map?Write a procedure to reduce K-maps.
- How do you express the Boolean function as a product of maxterms? Express the Boolean function F = xy + x′z in a product of maxterm form.
- Simplify the Boolean function: F(X,Y,Z) = ∑(0, 2, 4, 5, 6) using three variable K-map.
- Simplify the Boolean function F = A′B′C′ + B′CD′ + A′BCD′ + AB′C′ using K-map.
- Why don’t care conditions are used? Simplify F(w, x, y, z) = ∑(1, 3, 7, 11, 15) which has the don’t care conditions d(w, x, y, z) = ∑(0, 2, 5).
- Describe the forms of Boolean algebra with example.Define maxterms and minterms.

__Combinational Logic__

- What is combinational logic? Design a half adder logic using only NAND gates.
- Design the full subtractor circuit with using Decoder and explain the working principle.
- What do you mean by full adder and full subtractor? Design a half subtractor using only NOR gates.
- Design a full adder with truth table and logic gates.
- Explain parity generator and checker with suitable example.
- Describe BCD to excess-3 Code Conversion with truth table and logic diagram.
- What is combinational logic? What are its important features. Design a half adder logic using only NOR gate.

__Combination Logic with MSI and LSI__

- What is binary parallel adder? Describe 4-bit binary parallel adder with logic diagram.
- What is magnitude comparator? Design a logic circuit for 4 bit magnitude comparator and explain it.
- What is decimal adder? Explain it with truth table and logic diagram.
- What do you mean by decoder? Design a 3 to 8 line decoder using 2 to 4 line decoder and explain it.
- Differentiate between a MUX and a DEMUX. Draw a logic circuit of 8*1 multiplexer.
- Implement a full-adder circuit with a decoder and two OR gates.
- What is encoder? Design a 3 to 8 line decoder using two 2 to 4 line decoder and explain it.
- What is demultiplexer? Draw its block diagram and explain its working principle.
- Using a decoder and external gates, design the combinational circuit defined by the following three Boolean functions:

F1 = x′y′z + xz′ F2 = x′yz′ + xy′ F3 = xyz′ + xy

- Implement the following function Σ (0,1,3,4,8,9,10) using
- Decoder
- Multiplexer
- PLA

- Differentiate between PAL and PLA. A combinational circuit is defined by the functions:

F1(A, B,C) = ∑(3, 5, 6, 7) F2(A, B,C) = ∑(0, 2, 4, 7)

Implement the circuit with a PLA having three inputs, four product terms, and two outputs.

- Explain the PLA with the block diagram. Describe types of ROM in brief.

__Synchronous and Asynchronous Sequential Logic__

- Differentiate between combinational logic and sequential logic. List some applications of sequential logic.
- What is flip-flop? Mention the application of flip-flop.
- List the types of flip-flop.Describe the clocked RS flip-flop.
- How does a J-K flip flop differs from an S-R flip flop in its basic operations? Explain.
- Differentiate between Synchronous Sequential circuit and Asynchronous Sequential Circuit. What do you mean by D-flip-flop?
- What is master-slave flip-flop? Explain master slave J-K flipflop.
- What do you mean by triggering of flip flop? Define state table, state diagram and state equation.
- Explain design Procedure of clocked Sequential Circuit with suitable example.
- What is State reduction table? How JK flip flop can convert into a D-flip flop?

__Registers and counters __

- What do you mean by ripple counters? Explain the 4 bit ripple counter and also draw a timing diagram.
- What do you mean by shift registers? Mention the difference types of shift register.
- What is the difference between a serial and parallel transfer? Explain how to convert serial data to parallel and parallel data to serial. What type of register is needed?
- What do you mean by asynchronous counter? Design the mod-6 asynchronous counter and explain with truth table.
- What do you mean by synchronous counter?Design a 3 bit synchronous counter and explain it.
- What do you mean by counter? Design a counter as shown in the state diagram below

- Design the 4-bit synchronous up/down counter with timing diagram, logic diagram and truth table.
- Design a 3 bit synchronous counter and explain it.

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