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

Ans:-HOLD & HLDA.

17. 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.

18. List the four instructions which control the interrupt structure of the 8085 microprocessor.

Ans:-

• DI ( Disable Interrupts )
• EI ( Enable Interrupts )
• RIM ( Read Interrupt Masks )
• SIM ( Set Interrupt Masks )

19. What is meant by polling?

Ans:-Polling or device polling is a process which identifies the device that has interrupted the microprocessor.

20. What is meant by interrupt?

Ans:-Interrupt is an external signal that causes a microprocessor to jump to a specific subroutine.

21. 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. The priority of interrupts in 8085 is shown in the table.

22. What is a microcomputer?

Ans:-A computer that is designed using a microprocessor as its CPU is called microcomputer.

23. 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

24. 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

25. Steps involved to fetch a byte in 8085

Ans:-

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

26. 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

27. 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

28. 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

29. 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

30. 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.

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