Multiple Choice Questions & Answers on 8051 I/O Port Programming and Addressing Modes

1. Auto reload mode is allowed in which mode of the timer?

a) Mode 0

b) Mode 1

c) Mode 2

d) Mode 3

Answer: Mode 2

2. If Timer 0 is to be used as a counter, then at what particular pin clock pulse need to be applied?

a) P3.3

b) P3.4

c) P3.5

d) P3.6

Answer: P3.4

3. What is the maximum delay that can be generated with the crystal frequency of 22MHz?

a) 2978.9 sec

b) 0.011 msec

c) 11.63 sec

d) 2.97 msec

Answer: 2.97 msec

4. In the instruction “MOV TH1,#-3”, what is the value that is being loaded in the TH1 register?

a) 0xFCH

b) 0xFBH

c) 0xFDH

d) 0xFEH

Answer: 0xFDH

5. TF1, TR1, TF0, TR0 bits are of which register?

a) TMOD

b) SCON

c) TCON

d) SMOD

Answer: TCON

6. Find out the roll over value for the timer in Mode 0, Mode 1 and Mode 2?

a) 00FFH,0FFFH,FFFFH

b) 1FFFH,0FFFH,FFFFH

c) 1FFFH,FFFFH,00FFH

d) 1FFFH,00FFH,FFFFH

Answer: 1FFFH,FFFFH,00FFH.

7. What is the clock source for the timers?

a) some external crystal applied to the micro-controller for executing the timer

b) from the crystal applied to the micro-controller

c) through the software

d) through programming

Answer: from the crystal applied to the micro-controller

8. What is the function of the TMOD register?

a) TMOD register is used to set various operation modes of timer/counter

b) TMOD register is used to load the count of the timer

c) Is the destination or the final register where the result is obtained after the operation of the timer

d) Is used to interrupt the timer

Answer: TMOD register is used to set various operation modes of timer/counter

9. What is the frequency of the clock that is being used as the clock source for the timer?

a) some externally applied frequency f’

b) controller’s crystal frequency f

c) controller’s crystal frequency /12

d) externally applied frequency/12

Answer: controller’s crystal frequency /12

10. What steps are followed when we need to turn on any timer?

a) load the count, start the timer, keep monitoring it, stop the timer

b) load the TMOD register, load the count, start the timer, keep monitoring it, stop the timer

c) load the TMOD register, start the timer, load the count, keep monitoring it, stop the timer

d) none of the mentioned

Answer: load the TMOD register, load the count, start the timer, keep monitoring it, stop the timer

11. What are DPDT relays?

a) Single pole, single throw

b) Single pole, double throw

c) Double pole, double throw

d) None of the mentioned

Answer: Double pole, double throw

12. What is the principle on which electromagnetic relays operate?

a) electromagnetic induction

b) motor control

c) switching

d) none of the mentioned

Answer: electromagnetic induction

13. Why are solid-state relays advantageous over electromechanical relays?

a) they need zero voltage circuit

b) they need less current to be energised

c) they need less voltage to be energised

d) none of the mentioned

Answer: they need less current to be energised

14. Why do we need a ULN2803 in driving a relay?

a) for switching a motor

b) for increasing the current

c) for increasing the power

d) for switching the voltage

Answer: for increasing the current

15. What are optoisolators?

a) it is a driver

b) it is a thing isolated from the entire world

c) it is a device that can be used as an electromagnetic relay without a driver

d) none of the mentioned

Answer: it is a device that can be used as an

16. How can the direction of the DC motor be changed?

a) by changing the torque

b) by changing the switching speed

c) by changing the polarity of voltages connected to the leads

d) by changing the RPM rating

Answer: by changing the polarity of voltages connected to the leads

17. How can we change the speed of a DC motor using PWM?

a) By changing amplitude of PWM

b) By keeping fixed duty cycle

c) By changing duty cycle of PWM

d) By increasing power of PWM

Answer: By changing duty cycle of PWM

18. Which of the following can be a unit for torque?

a) kg/m2

b) ounce-inch

c) kg-m3

d) g/m

Answer: ounce-inch

19. How can we control the speed of a stepper motor?

a) by controlling its switching rate

b) by controlling its torque

c) by controlling its wave drive 4 step sequence

d) cant be controlled

Answer: by controlling its switching rate

20. The RPM rating given for the DC motor is for?

a) no-loaded

b) loaded

c) none of the mentioned

d) all of the mentioned

Answer: no-loaded