Gate 2005, 2006 and 2007 Questions on Microprocessor

Gate- 2005 Two marks Questions

Common data for Questions 10 and 11

Consider an 8085 Microprocessor system
The following program start at location 0100H.
                         LXI SP, 00FF
                         LXI H, 0107
                         MVI A, 20H
                         SUB M

Question 10. The content of accumulator when the program counter when the program counter reaches 0109H is
(a) 20H
(b) 02H
(c) 00H
(d) FFH

Answer: (c)

Explanation:

0100 LXI SP, 00FF
0103 LXI H, 0107
0106 MVI A, 20H
0108 SUB M
0109

M Contains the data of memory whose address which is in HL pair.
HL has address 0107
0107 corresponds to 20H.
therefore A-M=20H-20H = 00H

Question 11.

If in addition following code exists from 0109H onwards,
ORI 40H
ADD M

What will be the result in the accumulator after the last instruction is executed?

(a) 40H
(b) 20H
(c) 60H
(d) 42H

Answer: (c)

Explanation:
After 0109 Accumulator will contain 00H
ORI will execute OR operation between Accumulator and 40H and store the content to Accumulator A = 40H => 00H OR 04H
Now Adding M(20H) with A(40H) gives 60H.

Gate- 2006 Two mark questions

Question 12:

Following is the segment of the 8085 assemble language program
        LXI SP, EFFFH
          CALL 3000H
3000H: LXI H,3CF4H
PUSH PSW
SPHL
POP PSW
RET

On completion of RET execution, the contents of SP is
(a) 3CFOH
(b) 3CF8H
(c) EFFDH
(d) EFFFH

Answer: (b)

Explanation: