Short Question And Answer Microprocessor Set-15

1. List out the five categories of the 8085 instructions. Give examples of the instructions for each group.
Data transfer group – MOV, MVI, LXI.
Arithmetic group – ADD, SUB, INR.
Logical group –ANA, XRA, CMP.
Branch group – JMP, JNZ, CALL.
Stack I/O and Machine control group – PUSH, POP, IN, HLT.

2. Explain the difference between a JMP instruction and CALL instruction.
Ans: A JMP instruction permanently changes the program counter. A CALL instruction leaves information on the stack so that the original program execution sequence can be resumed.

3. Explain the purpose of the I/O instructions IN and OUT.
Ans: The IN instruction is used to move data from an I/O port into the accumulator. The OUT instruction is used to move data from the accumulator to an I/O port. The IN & OUT instructions are used only on microprocessor, which use a separate address space for interfacing.

4. What is the difference between the shift and rotate instructions?
Ans: A rotate instruction is a closed loop instruction. That is, the data moved out at one end is put back in at the other end. The shift instruction loses the data that is moved out of the last bit locations.

5. How many address lines in a 4096 x 8 EPROM CHIP?
Ans: 12 address lines.

6. What are the Control signals used for DMA operation?

7. What is meant by Wait State?
Ans:-This state is used by slow peripheral devices. The peripheral devices can transfer the data to or from the microprocessor by using READY input line. The microprocessor remains in wait state as long as READY line is low. During the wait state, the contents of the address, address/data and control buses are held constant.

8. List the four instructions which control the interrupt structure of the 8085 microprocessor.
DI ( Disable Interrupts )
EI ( Enable Interrupts )
RIM ( Read Interrupt Masks )
SIM ( Set Interrupt Masks )

9. What is meant by polling?
Ans:-Polling or device polling is a process which identifies the device that has interrupted the microprocessor.

10. What is meant by interrupt?
Ans:-Interrupt is an external signal that causes a microprocessor to jump to a specific subroutine

11. Explain priority interrupts of 8085.
Ans:-The 8085 microprocessor has five interrupt inputs. They are TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. These interrupts have a fixed priority of interrupt service. If two or more interrupts go high at the same time, the 8085 will service them on priority basis. The TRAP has the highest priority followed by RST 7.5, RST 6.5, RST 5.5.

12. What is the signal classification of 8085
Ans:-All the signals of 8085 can be classified into 6 groups
Address bus
Data bus
Control and status signals
Power supply and frequency signals
Externally initiated signals
Serial I/O ports

13. What are operations performed on data in 8085
Ans:- The various operations performed are
Store 8-bit data
Perform arithmetic and logical operations
Test for conditions
Sequence the execution of instructions
Store data temporarily during execution in the defined R/W memory locations called the stack

14. Steps involved to fetch a byte in 8085
i. The PC places the 16-bit memory address on the address bus ii. The control unit sends the control signal RD to enable the memory chip iii. The byte from the memory location is placed on the data bus iv. The byte is placed in the instruction decoder of the microprocessor and the task is carried out according to the instruction

15. How many interrupts does 8085 have, mention them
Ans:-The 8085 has 5 interrupt signals; they are INTR, RST7.5, RST6.5, RST5.5 and TRAP

16. Basic concepts in memory interfacing
Ans:-The primary function of memory interfacing is that the microprocessor should be able to read from and write into a given register of a memory chip. To perform these operations the microprocessor should
Be able to select the chip
Identify the register
Enable the appropriate buffer

17. Define instruction cycle, machine cycle and T-state
Ans:-Instruction cycle is defined, as the time required completing the execution of an instruction. Machine cycle is defined as the time required completing one operation of accessing memory, I/O or acknowledging an external request. Tcycle is defined as one subdivision of the operation performed in one clock period

18. What is an instruction?
Ans:-An instruction is a binary pattern entered through an input device to command the microprocessor to perform that specific function

19. What is the use of ALE
Ans:-The ALE is used to latch the lower order address so that it can be available in T2 and T3 and used for identifying the memory address. During T1 the ALE goes high, the latch is transparent ie, the output changes according to the input data, so the output of the latch is the lower order address. When ALE goes low the lower order address is latched until the next ALE.

20. How many machine cycles does 8085 have, mention them
Ans:The 8085 have seven machine cycles. They are
Opcode fetch
Memory read
Memory write
I/O read
I/O write
Interrupt acknowledge
Bus idle