Microcontroller Viva Questions and Answers

Project Viva Questions and answers from microcontroller:

Microcontroller Viva Questions and Answers

[1] What are the various criteria to choose the microcontroller?
The important criteria to be considered in choosing micro controllers are:
(1) Availability of software development tools like compilers, debuggers, assemblers
(2) Meeting the computing needs of the task at hand efficiently at low-cost.
(3) Wide availability
(4) Reliable sources/manufacturers
(5) The amount of RAM and ROM on chip
(6) The number of I/O pins and the timer on the chip
(7) Power consumption
(8) Speed of the device
(9) Packaging
(10) Cost per unit.

[2] List some of the 8051 microcontroller manufacturers?
Maxim/Dellas semiconductor

[3] What is difference between microprocessor and microcontroller?
The microprocessor has no ROM, RAM and no I/O ports on the chip itself.
Whereas the microcontroller has a CPU in addition to a fixed amount of RAM,ROM, I/O ports and a timer all on a single chip.

[4] List out some of the features of the 8051?
ROM -  4K bytes
RAM - 128 bytes
Timer - 2 no
I/O Pins - 32
Serial Port - 1
Interrupt sources - 6

[5] What are the various types of memories used in microcontroller/microprocessor?
ROM - Read Only Memory
RAM - Random Access Memory
PROM - Programmable Read Only Memory
EPROM - Erasable Programmable Read Only Memory
EEROM - Electrically Erasable Programmable Read Only Memory

[6] What is meant by Flipflop?
A Flip-flop is a basic electronic circuit used for storing information in a digital machine.
It is a bistable device. It means it has two stable states.
It has one or more inputs and two complement outputs.

Various definitions used in microprocessor/microcontrollers:

A semiconductor device manufactured using the LSI or VLSI technology. It has all the functions of Central Processing Unit (CPU), ie, ALU, Register arrays and control circuits of a computer.

Microcomputer: It is designed using microprocessor as its CPU. It has four component - microprocessor, memory unit, input and output devices.

Hardware : The physical components of the computer are called hardware.

Software: Set of instructions written for the computer to perform a task is called a program. Collection of such programs is called software.

Firmware: The software that is stored permanently in ROM, PROM or EPROM is called firmware.

Bit: The binary digits 0 and 1 are called bits.

Byte: Group of 8 bits is called a byte.

Nible: Group of 4 bits is called a nible. Also collection of two nibles is called a byte.

A group of bits that the computer recognises and processes at a time is called a word.The lenth of the word may varies from four bits to 32 bits. Here the 4 bits are used for small microprocessors and 32 bits are used for large computers like IBM 370.

A command formed using binary digits that are recognised and executed by the computer to perform as task. Group of one or more words forms an instruction.

Sequence of instructions that are written for the computer to perform a particular task is called as program.

The input or output devices that are connected to a microprocessor are called as peripherals. In some cases, memory is also considered as a peripheral.

Group of lines connecting the microprocessor with other components of a computer system is called a bus. It is a communication path over which electrical signals representing binary digits ( 0, 1) are transmitted. For a single bit to transmit, one line is used. The width of the bus is number of lines that are used to constitute that bus.

Data Bus:

  • Group of lines that transmit data in and out of the microprocessor is called the data bus.
  • Here the data can flow in both directions between the microprocessor and the peripheral devices.
  • Hence the data bus is bidirectional. The width of the data bus depends on the architecture of the microprocessor.
  • For an example, an 8 bit processor can operate on 8 bits of  data at a time and has a 8 bit wide data bus.

Address Bus:

  • Group of lines used by the microprocessor to send the address of the device or the memory location which the microprocessor needs to access.
  • The address bits flow in one direction, ie, from the microprocessor to the peripheral  devices.
  • Hence the address bus is unidirectional.
  • The width of the address bus determines the maximum number of memory locations that the microprocessor can access.


  • Using a single bus for two different functions is called multiplexing.
  • For an example, in 8085 microprocessor the low order 8 bits of the address and data are transmitted using AD7- AD0 lines.
  • These lines are also used as low order address bus during execution of instructions.
  • Thus the same lines are used for transmitting address and data.
  • This is called as multiplexing.
  • These lines are called as multiplexed address/data bus.

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4 Responses

  1. GUNASEKARAN says:

    QUESTION : What is the difference between synchronous, asynchronous and Interrupt driven data transfer?

    ANSWER : Let us take an example for each.

    Synchronous Mode : Take a case of boiling milk. In this mode the processor or controller continuously checks the status whether the milk is boiled or not ? in simple whether the task is completed or not ? so whats disadvantage here.

    All the processors efficient time wasted in only checking the status. it cannot concentrate on other tasks.

    Asynchronous Mode : Here the status is checked but not continuously. so some delay is made and then status is checked.

    Here comes Interrupt driven Mode: the most efficient one. why do i say this?

    Take an example: You are boiling some food in a cooker. when the rice is boiled the cooker blows whistle and tells us the rice is boiled. similarly when the task is completed interrupts informs micro controller. So one can concentrate on other works without looking the status of task.
    CPU efficient time is utilised.

  2. Kishori says:

    Can we connect DC motor directly to microcontroller??

  3. Nadeem Khan says:


    Suppose if i want to operate 20V power motor controlled by mCont, is it possible?

    Basics: Can i use high voltage peripherals controlled by low voltage mController??

    Please suggest.

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