Multiple Choice Questions & Answers on 8051 Microcontroller Interrupt Programming

1. Which pin of the external hardware is said to exhibit INT0 interrupt?

a) pin no 10

b) pin no 11

c) pin no 12

d) pin no 13

Answer: pin no 12

2. What are the contents of the IE register, when the interrupt of the memory location 0x00 is caused?

a) 0xFFH

b) 0x00H

c) 0x10H

d) 0xF0H

Answer: 0x00H

3. Which of the following combination is the best to enable the external hardware interrupt 0 of the IE register (assuming initially all bits of the IE register are zero)?

a) EX0=1

b) EA=1

c) any of the mentioned

d) EX0=1 & EA=1

Answer: EX0=1 & EA=1.

4. Which bit of the IE register is used to enable TxD/RxD interrupt?

a) IE.D5

b) IE.D2

c) IE.D3

d) IE.D4

Answer: IE.D4

5. What is the correct order of priority that is set after a controller gets reset?

a) RI/TI > TF1 > TF0 > INT1 > INT0

b) RI/TI < TF1 < TF0 < INT1 < INT0

c) INT0 > TF0 > INT1 > TF1 > RI/TI

d) INT0 < TF0 < INT1 < TF1 < RI/TI

Answer: INT0 > TF0 > INT1 > TF1 > RI/TI

6. When an interrupt is enabled, then where does the pointer moves immediately after this interrupt has occurred?

a) to the next instruction which is to be executed

b) to the first instruction of ISR

c) to a fixed location in memory called interrupt vector table

d) to the end of the program

Answer: to a fixed location in memory called interrupt vector table

7. After RETI instruction is executed then the pointer will move to which location in the program?

a) next interrupt of the interrupt vector table

b) immediate next instruction where interrupt is occurred

c) next instruction after the RETI in the memory

d) none of the mentioned

Answer: immediate next instruction where interrupt is occurred

8. What is the disadvantage of a level triggered pulse?

a) a constant pulse is to be maintained for a greater span of time

b) another interrupt may be generated if the low-level signal is not removed before the ISR is finished

c) it is difficult to produce

d) another interrupt may be caused if the signal is still low before the completion of the last instruction

Answer: another interrupt may be caused if the signal is still low before the completion of the last instruction

9. Which register is used to make the interrupt level or an edge triggered pulse?

a) TCON

b) IE

c) IPR

d) SCON

Answer: TCON

10. Why normally LJMP instructions are the topmost lines of the ISR?

a) so as to jump to some other location where there is a wider space of memory available to write the codes

b) so as to avoid overwriting of other interrupt instructions

c) all of the mentioned

d) none of the mentioned

Answer: all of the mentioned