Basics Of 8085 - Online Article

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.

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