Wednesday, November 4, 2009

Answer ALL questions.

PART A — (10 x 2 - 20 marks)

1. Sketch the schematic to generate separate read/write control signals for memory

and I/O related signals in 8085.

2. Calculate the execution time of an instruction MVI A, 82 H in 8085 runs at 2 MHz.

3. Write an assembly language progr am of 8085 to add two numbers stored in

memory locations 4040 H and 4041 H. Save the sum in location 4042 H.

4. Assume register B holds 93 H and the accumulator holds 15 H. Illustrate the

results of the instructions ORA B, XRA B and CMA.

5. Mention some of the applications of Rotate Instructions.

6. Design an 8-key input port with device address FF H using a 3 to 8 decoder to

interface with 8085.

7. How many interrupt sources are available in 8051? What are they?

8. Write short description on register bank registers and their uses.

9. What is called "read-modify-write"?

10. Why do you need a driver in between the microcontroller and the stepper motor?

PART B — (5 x 16 = 80 marks)


(i) Design an interfacing circuit using a 3-to-8 decoder to interface the 2732 EPROM

memory chip (4096 x 8), so that the memory address of this chip ranges from 0000 H

to 0 FFFH. (8)

(ii) Two machine codes 3E H and 32 H are stored in memory locations 2000 H and

2001 H respectively. The first machine code 3E H represents the opcode to load a data

byte in the accumulator and

the second code 32 H represents the data byte to be loaded in the accumulator.

Illustrate and explain the bus timings of 8085 as these machine codes are executed.



(b) (i)Describe an 8085 interrupt process. (8)

(ii) Write short notes on RST (RESTART) instructions. (8)

12.(a)Write down the comparison of

(i) Memory mapped I/O and peripheral I/O. (8)

(ii) CALL, RET and PUSH, POP instructions. (8)


(b) (i) Sixteen bytes of data are stored in memory locations at XX 50 H to XX 5F H.

Write a program to transfer the entire block of data to new memory locations starting

at XX 70 H. Using 8085 instructions. (8)

(ii) Registers BC contain 8538 H and registers DE contain 62A5 H. Write instructions

to subtract the contents of DE from the contents of BC and place the result in BC. (8)

13.(a) List the elements of the 8255 Programmable Peripheral Interface (PPI) and

explain its various operating modes. (16)


(b) With a block diagram of 8279 keyboard/display controller, explain its function.


14.(a) (i)Explain how the memory is organized in 8051 family of controller.


(ii) What are the functional blocks available in 8051? Explain with a block diagram.



(b) (i) How does the timer operate in 8051 in mode 2? Explain with suitable diagram.


(ii)Assuming XTAL = 11.0592 MHz, write a 8051 assembly language program to

generate a square wave of 50 Hz frequency on pin P 2.3. (8)

15. (a) (i) How many addressing modes ar e available in 8051? Explain them with

examples. (8)

(ii) Tabulate the program control instructions of 8051 and explain any five of them.



(b) (i) How do you interface a stepper motor to a controller? Give the necessar y

hardware and software functional blocks. (8)

(ii) Code a program to rotate stepper motor continuously using 8051. (8)

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