Technical Interview Question

8/7/2019 Technical Interview Question

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Technical Interview Question

1. What are the various registers in 8085? - Accumulator register, Temporary register,

Instruction register, Stack Pointer, Program Counter are the various registers in 8085 .

2. In 8085 name the 16 bit registers? - Stack pointer and Program counter all have 16 bits.

3. What are the various flags used in 8085? - Sign flag, Zero flag, Auxillary flag, Parity flag,

Carry flag.

4. What is Stack Pointer? - Stack pointer is a special purpose 16-bit register in the

Microprocessor, which holds the address of the top of the stack.

5. What is Program counter? - 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.

6. Which Stack is used in 8085? - LIFO (Last In First Out) stack is used in 8085.In this type

of Stack the last stored information can be retrieved first.

7. What happens when HLT instruction is executed in processor? - The Micro Processor

enters into Halt-State and the buses are tri-stated.

8. What is meant by a bus? - A bus is a group of conducting lines that carriers data,

address, & control signals.

9. What is Tri-state logic? - Three Logic Levels are used and they are High, Low, High

impedance state. The high and low are normal logic levels & high impedance state is

electrical open circuit conditions. Tri-state logic has a third line called enable line.

10. Give an example of one address microprocessor? - 8085 is a one address microprocessor.

11. In what way interrupts are classified in 8085? - In 8085 the interrupts are classified as

Hardware and Software interrupts.

12. What are Hardware interrupts? - TRAP, RST7.5, RST6.5, RST5.5, INTR.

13. What are Software interrupts? - RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.

14. Which interrupt has the highest priority? - TRAP has the highest priority.

15. Name 5 different addressing modes? - Immediate, Direct, Register, Register indirect,

Implied addressing modes.

16. How many interrupts are there in 8085? - There are 12 interrupts in 8085.

17. What is clock frequency for 8085? - 3 MHz is the maximum clock frequency for 8085.

18. What is the RST for the TRAP? - RST 4.5 is called as TRAP.

19. In 8085 which is called as High order / Low order Register? - Flag is called as Low order

register & Accumulator is called as High order Register.


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20. What are input & output devices? - Keyboards, Floppy disk are the examples of input

devices. Printer, LED / LCD display, CRT Monitor are the examples of output devices.

21. Can an RC circuit be used as clock source for 8085? - Yes, it can be used, if an accurate

clock frequency is not required. Also, the component cost is low compared to LC or

Crystal.

22. Why crystal is a preferred clock source? - Because of high stability, large Q (Quality

Factor) & the frequency that doesn?t drift with aging. Crystal is used as a clock source

most of the times.

23. Which interrupt is not level-sensitive in 8085? - RST 7.5 is a raising edge-triggering

interrupt.

24. What does Quality factor mean? - The Quality factor is also defined, as Q. So it is a

number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.

25. What are level-triggering interrupt? - RST 6.5 & RST 5.5 are level-triggering interrupts.

26. What are the flags in 8086? - In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zeroflag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.

27. What are the various interrupts in 8086? - Maskable interrupts, Non-Maskable

interrupts.

28. What is meant by Maskable interrupts? - An interrupt that can be turned off by the

programmer is known as Maskable interrupt.

29. What is Non-Maskable interrupts? - An interrupt which can be never be turned off

(ie.disabled) is known as Non-Maskable interrupt.

30. Which interrupts are generally used for critical events? - Non-Maskable interrupts are

used in critical events. Such as Power failure, Emergency, Shut off etc.,

31. Give examples for Maskable interrupts? - RST 7.5, RST6.5, RST5.5 are Maskable

interrupts

32. Give example for Non-Maskable interrupts? - Trap is known as Non-Maskable

interrupts, which is used in emergency condition.

33. What is the Maximum clock frequency in 8086? - 5 Mhz is the Maximum clock frequency

in 8086.

34. What are the various segment registers in 8086? - Code, Data, Stack, Extra Segment

registers in 8086.

35. Which Stack is used in 8086? - FIFO (First In First Out) stack is used in 8086.In this type

of Stack the first stored information is retrieved first.

36. What is SIM and RIM instructions? - SIM is Set Interrupt Mask. Used to mask the

hardware interrupts. RIM is Read Interrupt Mask. Used to check whether the interrupt

is Masked or not.


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37. Which is the tool used to connect the user and the computer? - Interpreter is the tool

used to connect the user and the tool.

38. What is the position of the Stack Pointer after the PUSH instruction? - The address line

is 02 less than the earlier value.

39. What is the position of the Stack Pointer after the POP instruction? - The address line is

02 greater than the earlier value.

40. Logic calculations are done in which type of registers? - Accumulator is the register in

which Arithmetic and Logic calculations are done.

41. What are the different functional units in 8086? - Bus Interface Unit and Execution unit,

are the two different functional units in 8086.

42. Give examples for Micro controller? - Z80, Intel MSC51 &96, Motorola are the best

examples of Microcontroller.

43. What is meant by cross-compiler? - A program runs on one machine and executes on

another is called as cross-compiler.44. Which Segment is used to store interrupt and subroutine return address registers? -

Stack Segment in segment register is used to store interrupt and subroutine return

address registers.

45. Which Flags can be set or reset by the programmer and also used to control the

operation of the processor? - Trace Flag, Interrupt Flag, Direction Flag.

46. What does EU do? - Execution Unit receives program instruction codes and data from

BIU, executes these instructions and store the result in general registers.

47. Which microprocessor accepts the program written for 8086 without any changes? - 8088

is that processor.

48. What is the difference between 8086 and 8088? - The BIU in 8088 is 8-bit data bus & 16-

bit in 8086.Instruction queue is 4 byte long in 8088and 6 byte in 8086.

49. What is a Microprocessor? - Microprocessor is a program-controlled device, which

fetches the instructions from memory, decodes and executes the instructions. Most Micro

Processor are single- chip devices.

50. Give examples for 8 / 16 / 32 bit Microprocessor? - 8-bit Processor - 8085 / Z80 / 6800; 16-

bit Processor - 8086 / 68000 / Z8000; 32-bit Processor - 80386 / 80486.

51. Why 8085 processor is called an 8 bit processor? - Because 8085 processor has 8 bit ALU

(Arithmetic Logic Review). Similarly 8086 processor has 16 bit ALU.

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

53. Define HCMOS? - High-density n- type Complimentary Metal Oxide Silicon field effect

transistor.


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54. What does microprocessor speed depend on? - The processing speed depends on DATA

BUS WIDTH.

55. Is the address bus unidirectional? - The address bus is unidirectional because the address

information is always given by the Micro Processor to address a memory location of an

input / output devices.

56. Is the data bus is Bi-directional? - The data bus is Bi-directional because the same bus is

used for transfer of data between Micro Processor and memory or input / output devices

in both the direction.

57. What is the disadvantage of microprocessor? - It has limitations on the size of data. Most

Microprocessor does not support floating-point operations.

58. What is the difference between microprocessor and microcontroller? - In Microprocessor

more op-codes, few bit handling instructions. But in Microcontroller: fewer op-codes,

more bit handling Instructions, and also it is defined as a device that includes micro

processor, memory, & input / output signal lines on a single chip.59. What is meant by LATCH? - Latch is a D- type flip-flop used as a temporary storage

device controlled by a timing signal, which can store 0 or 1. The primary function of a

Latch is data storage. It is used in output devices such as LED, to hold the data for

display.

60. Why does microprocessor contain ROM chips? - Microprocessor contain ROM chip

because it contain instructions to execute data.

61. What is the difference between primary & secondary storage device? - 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.

62. Difference between static and dynamic RAM? - Static RAM: No refreshing, 6 to 8 MOS

transistors are required to form one memory cell, Information stored as voltage level in a

flip flop. Dynamic RAM: Refreshed periodically, 3 to 4 transistors are required to form

one memory cell, Information is stored as a charge in the gate to substrate capacitance.

63. What is interrupt? - Interrupt is a signal send by external device to the processor so as to

request the processor to perform a particular work.

64. What is cache memory? - Cache memory is a small high-speed memory. It is used for

temporary storage of data & information between the main memory and the CPU (center

processing unit). The cache memory is only in RAM.

65. What is called ?Scratch pad of computer?? - Cache Memory is scratch pad of computer.

66. Which transistor is used in each cell of EPROM? - Floating gate Avalanche Injection

MOS (FAMOS) transistor is used in each cell of EPROM.


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67. Differentiate between RAM and ROM? - RAM: Read / Write memory, High Speed,

Volatile Memory. ROM: Read only memory, Low Speed, Non Voliate Memory.

68. What is a compiler? - Compiler is used to translate the high-level language program into

machine code at a time. It doesnt require special instruction to store in a memory, it

stores automatically. The Execution time is less compared to Interpreter.

69. Which processor structure is pipelined? - All x86 processors have pipelined structure.

70. What is flag? - Flag is a flip-flop used to store the information about the status of a

processor and the status of the instruction executed most recently

71. What is stack? - Stack is a portion of RAM used for saving the content of Program

Counter and general purpose registers.

72. Can ROM be used as stack? - ROM cannot be used as stack because it is not possible to

write to ROM.

73. What is NV-RAM? - Nonvolatile Read Write Memory, also called Flash memory. It is

also know as shadow RAM.


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QUESTION BANK

Subject Name: Microprocessors

Very short questionsQ1.What is a Microprocessor?

Q2.What is the difference between a Microprocessor and a CPU?

Q3. Define bit,byte,word and Instruction.

Q4. Discuss the function of ALU of 8085.

Q5. List four categories of 8085 Instructions that manipulate data.

Q6. What are the different Addressing Modes in 8085.

Q7.Why is Data Bus Bidirectional?

Q8. Specify four Control Signals commonly used by 8085 MPU.

Q9. What is the function of the Accumulator?

Q10. What are the various Registers of 8085?

Q11. Discuss Machine cycle and State.

Q12. What are the var8ious Status Flags provided in 8085?

Fill in the blanks:

Q13. Microprocessor 8085 is a ------------------ bit processor.

Q14. The Bus carries bits between Micropocessor and ------------------ .

Q15. Microprocessor has -------- number of pins.

Q16. Address bus of 8085 microprocessor is of -------- bits.

Q17. Data bus of 8085 microprocessor is of -------- bits.


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Q18. An Instruction has two parts: Opcode and the -------------.

Q19. The method of specifying an Operand is called--------------.

Q20. Examples of 1-byte instruction -------------------------.



Q23. STA 2500 H takes ------------------ machine cycles.

Q24. LDA 2500 H takes ------------------ machine cycles.

Q25. MOV A,B takes ------------------ machine cycles.

Q26. LXI H 2600 H takes ------------------ machine cycles.

Q27. ADI ,09 takes ------------------ machine cycles.

Q28. IN ,02 takes ------------------ machine cycles.

Q29. There are ------------- addressing modes.

Q30. Discuss the function of HOLD,READY in 8085.

Q31.What is an Interrupt?

Q32. What are various Interrupt lines in 8085?

Q33. Differentiate between microprocessors and microcontroller in one line.

Q34. PUSH PSW means --------------

Q35. POP PSW means -------------

Q36. The function of ALE is ----------------

Q37. Explain what is Vectored Interrupt.

Q38. Specify the crystal frequency required fo an 8085 system to operate at1.1 MHz.

Q39. What is an assembler.

Q40. RAM of 1K* 8 means --------------------


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Q41. There are --------------- opcodes in 8085.

Q42. Examples of direct addressing mode is -----------------.

Q43. Examples of indirect addressing mode is -----------------.

Q44. Examples of register addressing mode is -----------------.

Q45. Examples of implicit addressing mode is -----------------.

Q47. Examples of control signals of 8085 ----------------------.

Q48. Give the priority order of interrupts in 8085.

Q49. Data transfer instructions change the status of flags. State true or false.

Q50. CPM R means ------------------

Q51.The CPU of a computer comprises of ------------------.

Q52. Operand is a term used to refer as --------------.

Q53. An 8-bit microprocessor signifies that it has -----------------.

Q54. The address bus width of 64 KB of memory is ----------------.

Q55. DCR register can be used to decrement the contents of ----------------.

Q56. A 3-byte instrction requires ------------- fetch cycles for its execution.

Q57. A 2- byte instrction requires ------------- fetch cycles for its execution.

Q58. A 1-byte instrction requires ------------- fetch cycles for its execution.

Q59. The term cycle stealing is used for ---------------.

Q60. The instruction MOV A,B belongs to ----------------- addressing mode.

Q61. The instruction MVI A,B belongs to ----------------- addressing mode.

Q62. The instruction LXI H, 2000H belongs to ----------------- addressing mode.

Q63. The instruction LDAX D belongs to ----------------- addressing mode.

Q64. What is memory word size required in an 8085 system?


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Q65. Move the contents of register A to register B.

Q66. Move the contents of memory location 2000H to the accumulator directly.

Q67. List the sequence of events that occurs when 8085 MPU reads from memory.

Q68. Load the HL pair with the address 2500H.

Q69. Move the data 09H to the B register.

Q70. Specify the two 8085 signals that are used to latch data in an output port.

Q71. Complement the contents of the carry flag.

Q73. Rotate the contents of the accumulator by one bit to the left through carry.

Q74. What are the control signals necessary in the memory-mapped I/O?

Q75. What are various schemes of data transfer from CPU/memory to I/O devices?

Q76. What are different operating modes of 8255?

Q77. In a microprocessor based system, the address signals are sent by -------------.

Q78. In a microprocessor based system, the address bus is ---------------.

Q79. In a microprocessor based system,the data bus is ----------.

Q80. The basic purpose of timing and control unit is ------------------.

Q81.What are I/O ports in 8085?

Q82. TRAP is a maskable interrupt. State true or false.

Q83. Subroutine is defined as -----------------.

Q84. What are Instructions EI,DI in the 8085 Interrupt process?

Q85. List conditional Call and Return instructions.

Q86. Explain the sequence of a program execution when a subroutine is called &

executed.

Q87. What is stack pointer and explain their uses?


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Q88. What is Program counter and its uses?

Q90. The clock frequency required for 8085 is -----------.

Q91. Store the contents of accumulator in the memory location 2500H.

Q92. Increment the contents of memory location 2400H by 1.

Q93. What are the major differences between the 8080 and 8085 microprocessor?

Q94. Demonstrate the uses of instructions DAD,PCHL.

Q95. Decrement the contents of the register C by 2.

Q96. Explain the function of Data converters.

Q97. The instruction SPHL signifies -----------.

Q98. Explain the functions of Handshake signals.

Q99. List the elements of 8255A programmable peripheral interface.

Q100. List the operating modes of 8254 timer.

Short questions

Q1. Distinguish between Accumulator-Based and General Purpose Register BasedMicroprocessors.

Q2. Mention the differences between 8085 and 8086 Microprocessors.

Q3. Write a program to add two numbers of 8-bit each.

Q4.What are different types of memory?Explain.

Q5. Explain the need to demultiplex the bus AD7-Ado.

Q6. Write a program to count the number of 1s in a 8-bit number.

Q7. Expain the functions of ALE and IO/M signas in 8085.

Q8. Show the register contents as each of the following instructions is being executed


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MVI C, FFHLXI H, X X 70 H

LXI D, X X70 HMOV M, C

LDAX D

HLTQ9.Specify the contents of the accumulator and status of flags when followinginstructions are executed.

MVI A, B7H

ORA A

Q10.Explain following signals of 8085.

1) NOP2) HLDA

Q11. Explain the direct addressing modes and indirect addressing modes of

8085 with example.

Q12. Explain the control and status signals of 8085

Q13.Compare synchronous and asynchronous mode of data transfer.

Q14. With the help of SIM instruction format, write the instruction to mask RST5.5.

Q15. Explain the function of the 16-bit data transfer instruction LXI and of

instructon INX and DCX.

Q16. Explain stack and stack pointer.

Q17. Explain the difference between the bus cycle and the machine cycle.

Q18. Expain the RIM and SIM instruction.

Q19. Explain the following instruction:a) DAA

b) LDA ,16 bit addressc) STA ,16 bit address

Q20. Explain how information is stored and retrieved from stack using PUSH and

POP and the stack pointer.


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Q21. Explain the following Subroutines:

a) Multiple callingb) nestingc) common ending

Q22. Copmpare similarities between PUSH/POP and CALL/RET instructions.

Q23. List the eight steps to initiate and implement the 8085 interrupt.

Q24. What do you mean by polling.

Q25. How many bytes the following instructions of 8085 need?a) LDAb) JNZc) RALd)

MVI A

Q26. What do you mean by memory mapping?explain.

Q27.Explain how to connect multiple interrupts with the INTR interrupt line.

Q28. Differentiate between maskable and non maskable interrupts.

Q29. Explain the following instruction:a) ADD Mb) CMAc) CMP B

Q30. What are the functions of SID and SOD pins in 8085.

Q31.How are I/O devices addressed in 8085?

Q32. Explain features of the programmable interrupt controller,8259A with its block

diagram.

Q35. How to use RIM and SIM instruction for 8085.

Q36. What are hardware interrupts?Discuss TRAP interrupt.

Q37. Write a program to exchange the contents of memory location 2000 H with thecontents at memory location 2500 H.

Q38. Write a program to move the contents of memory location 2000H to

accumulator.Increment these contents and place then in location 2001H.


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Q39. Explain the function of READY signal of 8085

Q40. Set up 8155 timer to generate pulse after a given time delay

Q41. Explain block diagram of the 8279 Keyboard/Display interface and its

operations.

Q42.Explain the functions of the 8259A interrupt controller and its operations in fully

nested mode.

Q43. Explain the process of DMA and the functions of elements of 8237.

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Technical Interview Question