Microprocessor Interview Questions And Answers

8085 Microprocessor Questions:

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.
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

8086 Interview Questions:
1. What are the flags in 8086? - In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
2. What are the various interrupts in 8086? - Maskable interrupts, Non-Maskable interrupts.
3. What is meant by Maskable interrupts? - An interrupt that can be turned off by the programmer is known as Maskable interrupt.
4. What is Non-Maskable interrupts? - An interrupt which can be never be turned off (ie.disabled) is known as Non-Maskable interrupt.
5. Which interrupts are generally used for critical events? - Non-Maskable interrupts are used in critical events. Such as Power failure, Emergency, Shut off etc.,
6. Give examples for Maskable interrupts? - RST 7.5, RST6.5, RST5.5 are Maskable interrupts
7. Give example for Non-Maskable interrupts? - Trap is known as Non-Maskable interrupts, which is used in emergency condition.
8. What is the Maximum clock frequency in 8086? - 5 Mhz is the Maximum clock frequency in 8086.
9. What are the various segment registers in 8086? - Code, Data, Stack, Extra Segment registers in 8086.
10. 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.
11. What are the address lines for the software interrupts? -
RST 0 0000 H

RST1 0008 H

RST2 0010 H

RST3 0018 H

RST4 0020 H

RST5 0028 H

RST6 0030 H

RST7 0038 H

12. 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.
13. Which is the tool used to connect the user and the computer? - Interpreter is the tool used to connect the user and the tool.
14. What is the position of the Stack Pointer after the PUSH instruction? - The address line is 02 less than the earlier value.
15. What is the position of the Stack Pointer after the POP instruction? - The address line is 02 greater than the earlier value.
16. Logic calculations are done in which type of registers? - Accumulator is the register in which Arithmetic and Logic calculations are done.
17. What are the different functional units in 8086? - Bus Interface Unit and Execution unit, are the two different functional units in 8086.
18. Give examples for Micro controller? - Z80, Intel MSC51 &96, Motorola are the best examples of Microcontroller.
19. What is meant by cross-compiler? - A program runs on one machine and executes on another is called as cross-compiler.
20. What are the address lines for the hardware interrupts? -

RST 7.5 003C H

RST 6.5 0034 H

RST 5.5 002C H
TRAP 0024 H

21. 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.
22. 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.
23. What does EU do? - Execution Unit receives program instruction codes and data from BIU, executes these instructions and store the result in general registers.
24. Which microprocessor accepts the program written for 8086 without any changes? - 8088 is that processor.
25. 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.



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