Top 50 8051 Microcontroller MCQ – 2

Hi all, This is second part of 8051 microcontroller multiple choice questions series. In this MCQ series i have explained top 50 multiple choice questions. If you want to see more questions on 8051 microcontroller then check my previous post here.

This series will help in competitive exam like UPPCL- JE, SSC JE, RSEB, RRB and all competitive exam.

Please checkout all multiple choice questions like microcontroller, Power electronics, PLC and SCADA and 8086 microprocessor here. later I will add more questions in this series. So more update check frequently.

Question 1 Which of the following is the default value of stack once after the system undergoes the reset condition?

• 08H
• 09H
• 00H
• 07H

Answer: 07H

Question 2 Which of the following commands are used for addressing the off-chip data and associated codes respectively by data pointer?

• MOVC & MOVY
• MOVY & MOVB
• MOVZ & MOVA
• MOVX & MOVC

Answer: MOVX & MOVC

Question 3 Which of the following is the bit addressing range of addressable individual bits over the on-chip RAM?

• 00H to 7FH
• 01H to 7FH
• 00H to FFH
• 80H to FFH

Answer: 00H to 7FH

Question 4 ……….. signal control the flow of data

• DTR
• RTS
• Both 1 & 2
• None of the above

Answer: Both 1 & 2

Question 5 Register that is used to holds the memory address of the next instruction to be executed is

• Program Memory
• Program Counter
• Control Unit
• Instruction decoder

Answer: Program Counter

Question 6 If we say microcontroller is 8-bit then here 8-bit denotes size of

• Data Bus
• ALU
• Control Bus
• Address Bus

Answer: ALU

Question 7 Why microcontrollers are not called general purpose computers?

• Because they have built in RAM and ROM
• Because they design to perform dedicated task
• Because they are cheap
• Because they consume low power

Answer: Because they design to perform dedicated task

Question 8 What is the most appropriate criterion for choosing the right microcontroller of our choice?

• Speed
• Availability
• Ease with the product
• All of the mentioned

Answer: All of the mentioned

Question 9 A microcontroller at-least should consist of

• RAM, ROM, I/O ports and timers
• CPU, RAM, I/O ports and timers
• CPU, RAM, ROM, I/O ports and timers
• CPU, ROM, I/O ports and timer

Answer: CPU, RAM, ROM, I/O ports and timers

Question 10 AT89C2051 has RAM of

• 128 bytes
• 256 bytes
• 64 bytes
• 512 bytes

Answer: 128 bytes

Question 11 If we push data onto the stack then the stack pointer

• Increases with every push
• Decreases with every push
• Increases & decreases with every push
• None of the mentioned

Answer: Increases with every push

Question 12 How are the status of the carry, auxiliary carry and parity flag affected if the write instruction

MOV A,#9C

ADD A,#64H

• CY=0,AC=0,P=0
• CY=1,AC=1,P=0
• CY=0,AC=1,P=0
• CY=1,AC=1,P=1

Answer: CY=1,AC=1,P=0

Question 13 JZ, JNZ, instructions checked content of _______ register

• DPTR
• B
• A
• PSW

Answer: A

Question 14 Unlike microprocessors, microcontrollers make use of batteries because they have

• high power dissipation
• low power consumption
• low voltage consumption
• low current consumption

Answer: low power consumption

Question 15 Are PUSH and POP instructions are a type of CALL instructions?

• yes
• no
• none of the mentioned
• cant be determined

Answer: no

Question 16 What is the time taken by one machine cycle if crystal frequency is 20MHz?

• 1.085 micro seconds
• 0.60 micro seconds
• 0.75 micro seconds
• 1 micro seconds

Answer: 0.60 micro seconds

Question 17 What is the meaning of the instruction MOV A,05H?

• Data 05H is stored in the accumulator
• Fifth bit of accumulator is set to one
• Address 05H is stored in the accumulator
• None of the mentioned

Answer: Address 05H is stored in the accumulator

Question 18 The upper 128 bytes of an internal data memory from 80H through FFH usually represent _______

• General-purpose registers
• Special function registers
• Stack pointers
• Program counters

Answer: Special function registers

Question 19 Which of the ports act as the 16 bit address lines for transferring data through it?

• PORT 0 and PORT 1
• PORT 1 and PORT 2
• PORT 0 and PORT 2
• PORT 1 and PORT 3

Answer: PORT 0 and PORT 2

Question 20 Which operations are performed by the bit manipulating instructions of Boolean processor?

• Complement bit
• Set bit
• Clear bit
• All of the above

Answer: All of the above

Question 21 Which location specify the storage/loading of vector address during the interrupt generation?

• Stack Pointer
• Program Counter
• Data Pointer
• All of the above

Answer: Program Counter

Question 22 Which special function register play a vital role in the timer/counter mode selection process by allocating the bits in it?

• TMOD
• TCON
• SCON
• PCON

Answer: TMOD

Question 23 Why is it not necessary to specify the baud rate to be equal to the number of bits per second?

• Because each bit is preceded by a start bit & followed by one stop bit
• Because each byte is preceded by a start byte & followed by one stop byte
• Because each byte is preceded by a start bit & followed by one stop bit
• Because each bit is preceded by a start byte &followed by one stop byte

Answer: Because each byte is preceded by a start bit & followed by one stop bit

Question 24 Which is not the feature of 16-bit microcontroller?

• Large program & data memory spaces
• High speed
• I/O Flexibility
• Limited Control Applications

Answer: Limited Control Applications

Question 25 At what PIN number, there is EA pin which stands for External Access input?

• PIN 28
• PIN 29
• PIN 30
• PIN 31

Answer: PIN 31

Question 26 How does the microcontroller communicate with the external peripherals / memory?

• Via I/O ports
• Via register array
• Via memory
• All of the above

Answer: Via I/O ports

Question 27 What is the order decided by a processor or the CPU of a controller to execute an instruction?

• decode, fetch, execute
• execute, fetch, decode
• fetch, execute, decode
• fetch, decode, execute

Answer: fetch, decode, execute

Question 28 How are the performance and the computer capability affected by increasing its internal bus width?

• It increases and turns better
• It decreases
• Remains the same
• Internal bus width doesn’t affect the performance in any way

Answer: It increases and turns better

Question 29 How many bytes of bit addressable memory is present in 8051 based microcontrollers?

• 8 bytes
• 32 bytes
• 16 bytes
• 128 bytes

Answer: 16 bytes

Question 30 MOV A, @ R1 will:

• Copy R1 to the accumulator
• Copy the accumulator to R1
• Copy the contents of memory whose address is in R1 to the accumulator
• Copy the accumulator to the contents of memory whose address is in R1

Answer: Copy the contents of memory whose address is in R1 to the accumulator

Question 31 What is the file extension is used to load in a microcontroller to execute an instruction?

• .doc
• .c
• .txt
• .hex

Answer: .hex

Question 32 Which control signal/s is/are generated by timing and control unit of 8051 microcontroller in order to access the off-chip devices apart from the internal timings?

• ALE
• PSEN
• RD & WR
• All of the above

Answer: All of the above

Question 33 What is internal RAM memory of 8051 microprocessor?

• 32 bytes
• 64 bytes
• 128 bytes
• 256 bytes

Answer: 128 bytes

Question 34 How many timers/counter 8051 16-bit microprocessor have?

• 1
• 2
• 5
• 8

Answer: 2

Question 35 Which operator is the most important while assigning any instruction as register indirect instruction?

• $
• #
• @
• &

Answer: @

Question 36 Which of the following comes under the indexed addressing mode?

• MOVX A, @DPTR
• MOVC @A+DPTR,A
• MOV A,R0
• MOV @R0,A

Answer: MOVC @A+DPTR,A

Question 37 When we add two numbers the destination address must always be.

• Some immediate data
• Any register
• Accumulator
• Memory

Answer: Accumulator

Question 38 In 8 bit signed number operations, OV flag is set to 1 if:

• a carry is generated from D7 bit
• a carry is generated from D3 bit
• a carry is generated from D7 or D3 bit
• a carry is generated from D7 or D6 bit

Answer: a carry is generated from D7 or D6 bit

Question 39 Auto reload mode is allowed in which mode of the timer?

Mode 0
Mode 1
Mode 2
Mode 3

Answer: Mode 2

Question 40 What is the frequency of the clock that is being used as the clock source for the timer?

• Some externally applied frequency f’
• Controller’s crystal frequency f
• Controller’s crystal frequency /12
• Externally applied frequency/12

Answer: Controller’s crystal frequency /12

Question 41 Which of the following signal control the flow of data?

• RTS
• DTR
• RTS & DTR
• None of the mentioned

Answer: RTS

Question 42 Which of the following best describes the use of framing in asynchronous means of communication?

• It binds the data properly
• It tells us about the start and stops of the data to be transmitted or received
• It is used for error checking
• It is used for flow control

Answer: It tells us about the start and stops of the data to be transmitted or received

Question 43 What is the difference between UART and USART communication?

• They are the names of the same particular thing, just the difference of A and S is there in it
• One uses asynchronous means of communication and the other uses synchronous means of communication
• One uses asynchronous means of communication and the other uses asynchronous and synchronous means of communication
• One uses angular means of the communication and the other uses linear means of communication

Answer: One uses asynchronous means of communication and the other uses asynchronous and synchronous means of communication

Question 44 Which devices are specifically being used for converting serial to parallel and from parallel to serial respectively?

• Timers
• Counters
• Registers
• Serial communication

Answer: Registers

Question 45 Which pin of the external hardware is said to exhibit INT0 interrupt?

• pin no 10
• pin no 11
• pin no 12
• pin no 13

Answer: pin no 12

Question 46 Which bit of the IE register is used to enable TxD/RxD interrupt?

• IE.D5
• IE.D2
• IE.D3
• IE.D4

Answer: IE.D4

Question 47 When an interrupt is enabled, then where does the pointer moves immediately after this interrupt has occurred?

• to the next instruction which is to be executed
• to the first instruction of ISR
• to a fixed location in memory called interrupt vector table
• to the end of the program

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

Question 48 After RETI instruction is executed then the pointer will move to which location in the program?

• next interrupt of the interrupt vector table
• immediate next instruction where interrupt is occurred
• next instruction after the RETI in the memory
• none of the mentioned

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

Question 49 Which pin of the LCD is used for adjusting its contrast?

• pin no 1
• pin no 2
• pin no 3
• pin no 4

Answer: pin no 3

Question 50 For writing commands on an LCD, RS bit is

set
reset
set & reset
none of the mentioned

Answer: Reset

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