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Logic Design : Question Paper Jun 2014 - Computer Science Engg. (Semester 3) | Visveswaraya Technological University (VTU)

## Logic Design - Jun 2014

### Computer Science Engg. (Semester 3)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
1 (a) Define rise time, fall time in a digital waveform. What is the value of highly duty cycle (duty cycle H) if the frequency of a digital waveform is 5 MHz and the width of the positive pulse is 0.05μs?(4 marks) 1 (b) Realize the basic gates using only NAND gates.(6 marks) 1 (c) What is positive and negative logic? List the equivalences in positive and negative logic.(4 marks) 1 (d) Write a verilog HDL code using structural model for two input AND gate and prepare test-bench to simulate the circuit. Draw the timing diagram generated by simulating the verilog code. Assume 20 ns holding time of each input conbination.(6 marks) 2 (a) Simplify the Boolean function F(A,B,C,D)=∑m(1,3,5,7,8,10,12,14) by using Karnaugh map method and realize the logic circuit using only NAND gates,(6 marks) 2 (b) Draw Karnaugh map Y=F(A,B,C,D)=Πm(0,1,2,4,5,10)⋅ d(8,9,11,12,13,15) and get the simplified POS form of K-map.(4 marks) 2 (c) Get simplified expression of Y=F(A,B,C,D)=∑m(2,3,7,9,11,13)⋅d(1,10,15) using Quine-McClusky method.(10 marks) 3 (a) What is multiplexer? Design a 4-to-1 multiplexer using logic gates, write the truth table and explain its working principle.(6 marks) 3 (b) Describe the working principle of 3:8 decoder. Design a circuit that relizes the following functions using a 3:8 decoder and multi-input OR gates.
F1(A, B, C)=∑m(1,3,7)
F2(A, B, C)-∑m(2,3,5)
(6 marks)
3 (c) What is magnitude comparator? Design one bit comparator and write the truth table, logic circuit using basic gates,(6 marks) 3 (d) How does Programmable Logic Arrays (PLA) differ from a Programmable Array Logic (PAL)?(2 marks) 4 (a) With the help of neat diagram, explain the working of edge triggered JK flip-flop. Write the state diagram and excitation table.(6 marks) 4 (b) What is switch contact bounce? Explain the working principle of a simple RS latch debounce circuit.(4 marks) 4 (c) Write the state table and state diagram for the circuit shown in Fig.Q4(c). (10 marks) 5 (a) What is a shift register? Draw the logic diagram of a 4 bit serial in serial out (SISO) shift register using negative edge triggered JK or D flip-flop and explain its operation with the waveform to shift the binary number 1010 into the register,(8 marks) 5 (b) Explain with logic diagram the use of 8-bit SISO shift register in serial addition of two 8-bit numbers.(8 marks) 5 (c) Write verilog HDL code for 4-bit SIPO shift register when all the flip-flop outputs are available externally.(4 marks) 6 (a) What are asynchronous and synchronous counters? With a neat block diagram, output waveform and truth table, explain a 3-bit binary ripple counter constructed using negative edge triggered JK flip-flops.(10 marks) 6 (b) Design a mod-5 counter using JK flip-flops having the feature that if an unused state appears, the counter will reset to 000 at the next clock pulse.(10 marks) 7 (a) With neat block diagrams compare Mcaly model and Moore model of sequential logic system.(4 marks) 7 (b) Draw the ASM chart for the Mcaly machine shown in fig.Q7(b). (8 marks) 7 (c) Using row elimination method reduce the state diagram shown in fig.Q7(c). (8 marks) 8 (a) What is the binary ladder? Explain the binary ladder with a digital input of 1000.(6 marks) 8 (b) Defne Accuracy and Resolution with respect to DAC.(4 marks) 8 (c) With a neat circuit diagram, explain parallel ADC.(10 marks)

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