Get your PIC & 8051 Microcontroller viva sorted by just 21 questions

8051 microcontroller

The PIC & 8051 microcontroller is quite a task when it comes to its preparation for the viva or interview. Don’t worry!!!!!

You are not struggling alone with this issue

Thus we are here to help you all to get the gag done by just referring to 21 questions. It covers all of the essential questions that could be asked by the external or the mentor related to pic and 8051 microcontroller

Questions on PIC & 8051 microcontroller

Types of Microcontroller Architecture

Von Neumann Architecture— CISC

  • Uses one memory space for program instructions and data
  • Limits operating bandwidth
  • Execution of data and code occurs in a sequential fashion
  • Reduced Speed of Operation

Harvard Architecture — RISC

  • Uses two separate memory spaces for program instructions and data
  • Improved operating bandwidth
  • Improved Sped of Operation

What is selection Criteria for 8051 microcontroller or any in general

  • Data Handling Capacity- Bits, Nibble Bytes, Words
  • Speed
  • Amount of RAM/ ROM/ EPROM
  • Number of I/O pins, Timers
  • Power consumption
  • Easy to upgrade –Higher Performances or low power operations
  • Added features like ADC/ DAC
  • Availability of Software and Hardware Development Tools:- Assembler, Compilers, Debuggers, Emulators

Feature of 8051 Microcontroller

  • It is an 8-bit microcontroller, fabricated by HMOs technology.
  • Has 16-bit address bus
  • Operates on 11.095 MHz MHz clock frequency
  • 128- bytes of RAM
  • 4K of ROM
  • 34 general-purpose registers each of 8 bits [4 banks] + A,B
  • 21 Special Function Registers
  • 16-bit timers/ counters
  • 3 internal and 2 external interrupts.
  • Bit as well as byte-addressable RAM area of 16 bytes.
  • Four, 8-bit ports– 32 I/O lines
  • 16-bit program counter, Data Pointer, and 8 bit Stack pointer

What is PIC

PIC (Peripheral Interface Controller) is an 8-bit microcontroller by Microchips.
It uses CMOS technology for High performance, low cost, and small size.
It uses RISC architecture

Feature of PIC

  • It uses RISC architecture
  • 8-bit data bus
  • 16-bit instructions
  • DC-40 MHz clock Input
  • 2MBytes of program ROM [21 Address line]
  • 4KBytes of Data RAM [12 Address lines]
  • 32 K flash ROM
  • 1536 bytes SRAM –Scratch Pad
  • 256 bytes – EEPROM
  • Priority Level Interrupts
  • Wide operating voltage Range
  • 5 ports A[6], B,C,D[8], E[3] =33
  • 10 bit, 8/13 channel ADC
  • Three External Interrupt Pins
  • Has 16 bank registers with 256 entries each.
  • 4 timer/counters
  • operates in a bit, byte, and word
  • support USART to communicate serially

PIC Architecture

PIC microcontrollers use Harvard Architecture for their designing which include:

  • Microprocessor unit (MPU) –
  • Program memory for instructions
  • Data memory for data
  • I/O ports
  • Support devices such as timers, ADC, etc.
  • Support for serial communication

Types of Mode in PIC

  • Sleep
  • run
  • Idle

What is a Microprocessor unit

MCU consists of ALU (Arithmetic logic unit), registers, and control unit.

what is ALU

ALU consists of Working Register, Status register, and instruction decoder

The function of the ALU is While performing the operation on ALU one of the operands is from the program data memory which is multiplex with other input from SFRS and which in turn is given to ALU along with the working register (W). The result of the operation may be stored either in the working register or file register according to the direction bit ‘d’.
if d = 0 = W register
d= 1 = FSR

What is PSW

It is an 8-bit Program Status word register
It consists of 1-bit flags that are used to store the result of an arithmetic operation.
e.g. – CY, AC, OV, P, RS1, and RS0

Registers in PIC

Bank Select Register (BSR) – These 4-bit registers are use by direct mode of addressing for the data memory
File Select Registers (FSRs)- These 16-bit registers are use as memory pointers in the indirect mode of addressing the data memory
Program Counter (PC)- It is a 21-bit register that holds the program memory address while executing an instruction.
Indirect File Register (INDF) – Indirect addressing in support of FSR

Data Memory

  • Data Memory up to 4k bytes
  • It has a Data register map with a 12-bit address bus starting from memory address 000 to FFF
  • Divided into 256-byte banks
  • There are a total of F banks
  • Half memory of bank 0 and a half memory of bank 15 together form a virtual bank which is attainable no matter which bank is select
  • BSR is use to select the bank
  • However, the machine code for a PIC18 instruction only has 8 bits assigned for a data memory address while it needs 12 bits. Thus the Bank Select Register (BSR) supplies the other 4 bits as
  • There are 3 FSR each compose of two parts FSRH and FSRL

What is Stack

A stack works on Last In, First Out ( LIFO ) data structure
Stacks are a type of register use to temporarily store data in memory (RAM) while executing an instruction.
When data is added to the stack it is said to be pushed on the stack; When the item leaves the stack, it is said to be pulled out the stack.
PIC 18F4558 has 31 , 21- bit stacks
Stack points to the last used location,

what is reset?

Puts the controller to the initial value by causing all of the current data to be missing.

Types of reset

  • Power-on Reset (POR)
  • Power-up Timer (PWRT)
  • Oscillator Start-up Timer (OST)

What is MCLR

The MCLR pin provides a way for triggering ON an external reset of the microcontroller device. This reset is enabled by putting the pin low.

However, these types of devices usually consist of a noise filter in their Reset path which detects and neglects small pulses.

What is a power-on reset

A Power-on Reset pulse is developed on-chip when VDD rise is detected above the threshold.

what is a power-up timer

The power-up timer is a special type of timer that is use to generate delays at the beginning of program execution after the PIC is reset on the power-up

what is brownout detect

This is the circuitry that is develop in the microcontroller to keep an eye n the changing voltage level throughout the execution of a program.

What is a watchdog timer

Watchdog timer (WDT) is a type of timer that allows us to reset the processor if the program gets jam in an unknown state (e.g. infinite loop)

What is a Real-Time clock

The purpose of RTC is to provide accurate times and dates for various operations.


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Have a good day 🙂

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