Sunday, March 6, 2016


B.E (Full Time) DEGREE END SEMESTER EXAMINATIONS, APRIL / MAY 2014, Computer Science and Engineering, Second Semester, CS 8201 – DIGITAL PRINCIPLES AND SYSTEM DESIGN

Academic Year
April May 2014
Subject Code

CS 8201

Subject Name

Digital Principles and System Design

Computer Science and Engineering
Second Semester

Computer Science and Engineering
Second Semester
(Regulation 2012)
Time : 3 Hours                      Answer A L L Questions                Max. Marks 100
PART-A (10 x 2 = 20 Marks)

1. Convert the hex number F3A2 to binary and octal.
2. Show that that the excess -3 code is self complementing.
3. Is the NAND function associative? Justify.
4. The main stairway in a block of flats has three switches for controlling the lights. Switch A is located at the top of the stairs, switch B is located halfway up the stairs and switch C is positioned at the bottom of the stairs. Design a combinational circuit to control the lights on the staircase.
5. Give the HDL description of a positive edge triggered JK flip flop.
6. Show how timing signals can be generated using a binary counter and a decoder.
7. What is an essential hazard?
8. Comment on the circuit whose transition table is shown below:

9. What is an FPGA?
10. Differentiate between a PLA and a PAL.

PART-B (5x16 = 80 Marks)

11. (i) Simplify F(A,B,C,D) = ∑(1,2,3,5,6,7,10,11), d(A,B,C,D) = ∑(9, 12, 15) using Karnaugh map. Draw the logic diagram using NAND gates only. (8)
(ii) Simplify the Boolean expression F (A, B, C, D) = B+BCD+B'CD+AB+A'B+B'C. Indicate the theorems used. (4)
(iii) Express the following function as a sum of minterms and as a product of maxterms: F (A.B.C.D) = B'D+A'D+BD. (4)
12. a) (i) Discuss the principle of operation of carry-look ahead adders. Design a 4-bit carry-look ahead adder and draw the circuit. Calculate the delay for generating s3 and c4. (10)
(ii) Design a 3x3 binary multiplier circuit. (6)
b) (i) Design a four-input priority encoder with the D0 input having the highest priority and the D3 input having the least priority. (10)
(ii) Write a Verilog HDL model for the priority encoder given above. (6)
13. a) (i) Design a counter with the following repeated binary sequence: 0, 1, 3, 5, 7, 0, … Use J-K flip flops. (10)
(ii) Draw the circuit of a four-bit universal shift register and discuss its operation. (6)
b) (i) Discuss the design of a 4-bit up/down binary ripple counter using T flip flops. (10)
(ii) Reduce the number of states in the following state table and tabulate the state table:

Starting from state a and the input sequence 01100010001, determine the output sequence for the original state table and the reduced state table. Compare the results. (6)
14. a) For the two-input, two-output system, whose primitive flow table is shown below, perform the following: (4+2+2+2+6)
• Merge the flow table by finding all compatible pairs using an implication table
• Find the maximal compatibles through a merger diagram
• Find the minimal set of compatibles that cover-s all the states and is closed
• Do a race-free state assignment
• Design the circuit

b) (i) An asynchronous sequential circuit is described by the excitation function
Y = x1x2' + (x1+ x2' )y
and the output function z = y.
Draw the logic diagram of the circuit. (2)
Derive the transition table and output map. (4)
Obtain a flow table for the circuit. (2)
Describe the behavior of the circuit. (2)
(ii) What is a static hazard? Discuss with examples. Find a circuit that has no static hazards and implements the Boolean function
F(A,B,C,D) = (3,4,5,6,11,12,13,14,15) (6)
15. a) (i) Give the logic diagram of a basic RAM cell and discuss.
Show how a 64K X 8 RAM can be constructed, indicating all the connections and the decoding logic required. Use two-dimensional decoding. (10)
(ii) A 12-bit Hamming code word containing 8 bits of data and 4 parity bits is read from memory. What was the original 8-bit data word that was written into memory, if the 12-bit word read out is as follows: (6)
1. 000011101010
2. 101110000110
b) (i) Discuss the construction of a typical ROM.
What are t he different types of ROM?
Show how a ROM can be used to implement a combinational circuit that finds the nine's complement of a BCD digit. (10)
(ii) Show how the following functions can be implemented using a PLA: (6)
F1 (A.B.C.D) = 2,3,6,7,11,15 and F2 (A.B.C.D) = 0,2,4,6,8,9,11,12,13,15


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