Microprocessors Interview Questions and Answers:

1. What is a Microprocessor?

Ans. Microprocessor is a program-controlled device, which fetches the instructions from memory, decodes and executes the instructions.

2. What is microcontroller?

Ans. Microcontroller is a device that includes microprocessor, memory and I/O signal lines on a single chip, fabricated using VLSI technology.

3. What is a microprocessor and how microcomputer is different from a microprocessor?

Ans. A microprocessor is an LSI (large scale integration) chip that is capable of performing arithmetic and logic functions as defined by a given program and a computer built with a microprocessor is called a microcomputer.

4. What is 1st/2nd/3rd/4th generation processor?

Ans. The processor made of PMOS/NMOS/HMOS/HCMOS technology is called 1st/2nd/3rd/4th generation processor, and it is made up of 4/8/16/32 bits.

5. Give examples for 8/16/32 bit microprocessors?

Ans. Examples of 8/16/32 bit microprocessors are: 8-bit processor-8085/Z80/6800; 16-bit processor-8086/68000/Z8000; 32-bit processor-80386/80486.

6. What is Hardware and Software?

Ans. The physical components of the system i.e. computer are called Hardware. Group of programs is called software.

7. What is Assembly Language?

Ans. A medium of communication with a computer in which programs are written in mnemonics. Binary instructions are given abbreviated names called mnemonics, which form the assembly language for a given processor.

8. What is Machine Language?

Ans. The binary medium of communication with a computer through a designed set of instructions specific to each computer.

9. What is Central Processing Unit (CPU)?

Ans. CPU is a heart of the computer. Central Processing Unit controls the operation of the computer. In a microcomputer the CPU is a microprocessor. The CPU fetches binary coded instructions from memory, decodes the instructions into a series of simple actions and carries out these actions in a sequence of steps.

10. What is meant by a bus?

Ans.  A bus is a group of conducting lines that carries data, address and control signals.

11. What is Address Bus?

Ans. The address bus consists of parallel signal lines on which the CPU sends out the address of the memory location that is to be written to or read from. The number of memory locations that the CPU can address is determined by the number of address lines.

12. What is Data Bus?

Ans. The data bus consists of parallel signal lines. The data bus lines are bi-directional. This means that the CPU can read data in from memory or from a port on these lines, or it can send data out to memory or to a port on these lines.

13. What is the difference between primary and secondary storage device?

Ans. In primary storage device the storage capacity is limited. It has a volatile memory. In secondary storage device the storage capacity is larger. It is a nonvolatile memory. Primary devices are: RAM/ROM. Secondary devices are: Floppy disc/Hard disk.

14. What is clock frequency for 8085?

Ans. 3 MHz is the maximum clock frequency for 8085.

15. What are the various registers in 8085?

Ans. Various registers in 8085 are Accumulator, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085.

16. List the control and status signals available in 8085.

Ans. Control and status signals available in 8085 are ALE, RD, WR, IO/M, S0, S1.

17. What is the function of signals at pin marked IO/M̅ in 8085 microprocessor?

Ans. This is a status signal used to differentiate between I/O and memory operations. When the signal at this pin is HIGH, data transfer takes place between microprocessor and I/O devices and when the signal at this pin is LOW, data transfer takes place between microprocessor and the memory.

18. In 8085 name the 16 hit registers?

Ans. Stack pointer and Program counter all have 16 hits.

19. What is Program counter?

Ans. Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched, Also Program register keeps the address of the next instruction.

20. What is Stack Pointer?

Ans. Stack pointer is a special purpose 16-bit register, which holds the address of the top of the stack.

21. For 8085 microprocessor, if the stack pointer points to 0000H, in which memory location will stack contents be stored, if the stack is to be used?

Ans. While storing stack contents, the stack pointer always first decrement and then the memory location pointed by the stack pointer is filled up. After decrementing 1 from 0000H, FFFFH is obtained, therefore, stack contents will be stored from the memory location FFFFH onwards on progressively decreasing memory location addresses.

22. What is a flag?

Ans. The data conditions, after arithmetic or logical operations, are indicated by setting or resetting the flip-flops called flags.

23. What are the various flags used in 8085?

Ans. Various flags used in 8085 are Sign flag, Zero flag, Auxiliary flag, Parity flag, Carry flag.

24. Explain why an interrupt controller is required with micropro­cessor systems. How many interrupts can be handled by one chip?

Ans. Interrupts can be used for a variety of applications. Each of such interrupt applications need a separate interrupt input. For 8085 we have five interrupt pins whereas in case of 8086 there is only one interrupt pin. For applications where processor interrupts are sufficiently large external device, called the programmable interrupt controller, is to be used. 8259 A is a commonly used priority interrupt controller.

Primary Features of 8259 A. It is a programmable interrupt-managing device specially designed for use with interrupt signals of the 8085 microprocessor. Its primary features are:

  1. It manages eight interrupts.
  2. By cascading nine 8259s, it is possible to have 64 priority interrupts.
  3. Interrupts can mask or unmask individually.
  4. Interrupt mask register makes it possible to mask individual interrupt request.

25. Why is the Z-flag of a 8085 microprocessor not affected after execution of the instruction MOV D, B?

Ans. In 8085 microprocessor, zero flag is used to indicate the result of arithmetic or logic operation of ALU—zero or non-zero. The zero flag is set when the result is zero and reset in case result is non-zero. Zero flag of a 8085 microprocessor is only affected after ALU operation of microprocessor. Since MOV D, B is not an ALU operation, zero flag is not affected.

26. In what way interrupts are classified in 8085?

Ans. In 8085 the interrupts are classified as Hardware and Software interrupts.

27. What are Hardware interrupts?

Ans. Hardware interrupts are TRAP, RST7.5, RST6.5, RST5.5, INTR.

28. What are Software interrupts?

Ans. Software interrupts are RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.

29. Which interrupt has the highest priority?

Ans. TRAP has the highest priority.

30. Name 5 different addressing modes in 8085?

Ans. Different addressing modes in 8085 are Immediate, Direct, Register, Register indirect, Implied addressing modes.

31. Write down the addressing modes of the following instructions: (i) ACI 20H (ii) CMA (iii) STA 2500H (iv)LXIH, 2005H (v) XCHG (vi) MOV E, L.


32. What are the advantages in using a microprocessor in an instrument?

Ans. The advantages of using a microprocessor in an instrument are (i) reduced size (ii) more reliability (iii) elimination of drift of analog circuits and (iv) changes in design of the system is not a cause for total redesign of the system.

33. What are the applications of microprocessor ?

Ans. Microprocessors find wide applications in the fields of instrumentation, communication, data processing, industrial process instrumentation, commerce and consumer products.

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