Birla Institute of Technology and Science, PilaniDistance Learning Programs Division

MS Software Engineering in Collaboration with Wipro TechnologiesFirst Semester 2003 – 2004

Comprehensive Exam

Course No. : SEWP ZG 261Course Name:- Digital Electronics & MicroprocessorsNature of Exam :- Open Book ExamMax Marks :- 60 Duration : 3 HoursDate:- 25-01-2004

Note: Please read the instructions on the first page of the main answer book Please fill in the required details on the main answer book as soon as it’s given to

you(Name, BITS ID No, Course Name,Course No. Day and Date,Name of Exam) Please Write No. of extra sheets used in the space marked “ No of supplementary

Copies attached” on the main sheet.

Answer all questions. All questions carry equal marks.

1. Design a ‘synchronous counter’ that goes through the sequence

1 3 5 7 4 2 0 6 and repeat. Use D Flip-flops

a. Write state table. (2 marks)b. Write K-maps for flip flop input equation. (2 marks)c. Write logic diagram. (2 marks)

2. A Step in space vehicle check out depends on four sensors. Every circuit is functioning properly if the sensor number 2 and at least two sensors of the other three are at logic 1. If the circuit is not working properly an alarm should sound. Design the simplified digital circuit and realize using gates.

3. Consider the given function below:f(A,B,C,D) = m( 0,1,2,4,5,7,11,15)

a. Realize the above function using an 8-1 MUX with control inputs ACD (3 marks)

b. Realize using a 4-1 MUX and logic gates with control inputs AC. (3 marks)

4. Design a sequential circuit with two D flip flops A and B and one input x When x =0 the state of the circuit remains the same, when x=1 the circuit goes through the state transitions from 00 to 11 to 10 back to 00 and repeats.

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a. Write state table. (2 marks)b. Write k maps and Boolean equations for inputs to flip flops (2 marks)c. Draw the logic dia. (2 marks)

5. We have a decoder with three inputs a, b and c and eight active low outputs labeled 0 through 7. In addition there is an active low enable input ~EN’. We wish to implement the following function using decoder and as few NAND gates as possible

Show the block diagram F( a, b, c, e) = Σ m ( 1, 3, 7, 9, 15)

6. a. Specify the register contents and flag status as the following instructions are executed. (3 marks)

SUB A A B S Z C YMOV B,ADCR BINR BSUI DIHHLT

b. Specify the register contents and flag status as the following instructions are executed. (3 marks)

MVI A, 5EH A C S Z C YADI A2HMOV C, AHLT

7. Write a 8085 program to meet the following specifications;

a. Initialize the stack pointer register at 8999H. (1.5 marks)b. Clear the memory contents starting from 9790 to 979FH (1.5 marks)c. Load register pairs B,D,H with data 0237H, 1242H and 4087H respectively.

(1.5 marks)d. Push the contents of register pair B,D and H on stack. (1.5 marks)

8. Explain how a square wave can be generated using 8253 with neat diagrams and program.

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9. Determine the control words necessary to put an 8255 in mode 0 with the following configuration.

a. port a input ;; ports b and c output. (1.5 marks)b. port a and c lower o/p ;; port b and c upper input (1.5 marks)c. port a and c upper input ;; port b and c lower output (1.5 marks)d. ports a and b input ;; port c output (1.5 marks)

10. Read the following program and answer the questions given below.

LXI SP, 0500HLXI B, 3055HLXI H, 22FFHLXI D, 3090HPUSH HNOPPUSH BNOPMOV A, LHLT

a. What is stored in stack pointer register after the execution of the first instruction. (1.5 marks)

b. What is the memory location of stack where the first data byte will be stored. (1.5 marks)

c. What is stored in memory location 04FEH when PUSH H is executed. (1.5 marks)

d. After the execution of PUSH H what is the address in the stack pointer register and what is stored in stack memory location 04FDH. (1.5 marks)

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