Short Question And Answer Microprocessor Set-12

1. What happens when the 8085 execute the out instruction?
When the 8085 executes the out instruction, in the third machine cycle, it places the output port address on the low-order address bus, duplicates the same port address on the higher order address bus, places the contents of the accumulator on the data bus and asserts the control signal WR.

2. How will the port number be affected if we decode the high-order address lines
A15 –A8 rather than A7 – A0?
The port address will remain the same because the I/O port address is duplicated on both segments of the address bus.

3. Define Memory mapped I/O?
Instead of a memory register, if an output device is connected at the address, the accumulator contents will be transferred to the output device. This is called memory mapped I/O.

4. What is an interrupt I/O?
The interrupt I/O is a process of data transfer whereby an external device or a peripheral can inform the processor that it is ready for communication and it requests attention

5. What is Partial Decoding?
The output port can be selected by decoding some of the address lines is called partial decoding .

6. Define absolute decoding?
All the eight lines are decoded to generate one unique output pulse. This is called absolute decoding.

7. Give the characteristics of Memory mapped I/O?
Execution speed
Data transfer
Device address

8. What is SIM?
SIM: Set interrupt Mask. It is a 1-byte instruction. Used for three functions
a. To set the Mask
b. To reset the flip flop
c. Implement the I/O

9.What is RIM?
RIM: Read Interrupt Mask Used for three functions
a. To read interrupt mask
b. To identify the pending interrupt
c. To receive serial data

10. What the two categories of an interrupt?
Four Maskable interrupt
One Non Maskable interrupt

11. What is the purpose of an interrupt enable?
The instruction Enable Interrupt sets the Interrupt Enable flip-flop and enables the interrupt process

12. Write an instruction to enable all the interrupts in an 8085 system?
MVI A,08H .

13. Give the commonly used priority modes?
Fully Nested mode
Automatic rotation mode
Specific rotation mode

14. What do you mean by control logic?
This has two pins. INT as an output, and INTA as an input. The INT is connected to the interrupt pin of the MPU.

15. What are the two modes of DMA execution?
Slave Mode, Master mode

16. How the 8327 DMA controller transfers 64K bytes of data per channel with
The most significant bits D15 and D14 of the count register are used to specify DMA function and the remaining fourteen bits are used to specify the number of bytes to be transferred.

17. Give the three formats of END of Interrupt?
NON-specific EOI command
Specific EOI command
Automatic interrupt

18. What are the signals used by the DMA controller?
The Signals are:

  • HLDA
  • DMA request
  • DMA acknowledge
  • AEN – address enable
  • ADSTB- address strobe

19. Give the additional features of 8259A controller?

  • Input triggering
  • Interrupt Status
  • Poll Method

20. How the signals of the 8237 are classified?
The signals are classified in to two groups.
i. One group of signals are used for interfacing with the MPU
ii. Second group for communicating with the peripherals.