Two Marks Questions with Answers

Two Marks Questions with Answers

Q.l What is meant by wait state ?

Ans. : This state is used by slow peripheral devices. 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.

Q.2 Give the steps involved in fetching a byte in 8085.

Ans. :

• The PC places the 16-bit memory address on the address bus

• The control emit sends the control signal   to enable the memory chip

• The byte from the memory location is placed on the data bus

• The byte is placed in the instruction decoder of the microprocessor and the task is carried out according to the instruction.

Q.3 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.

T-cycle is defined as one subdivision of the operation performed in one clock period.

Q.4    How many machine cycles are needed to execute STA 1800 ?

Ans. : Four machine cycles are needed to execute STA 1800 instruction.

Q.5    What are the different machine cycles in 8085 microprocessor ?

Ans. : The different machine cycles in 8085 microprocessor are :

1. Opcode fetch   

2. Memory read

3. Memory write 

4. I/O read

5. I/O write

6. Interrupt acknowledge

7. Bus idle

Q.6 List out the machine cycles for executing the instruction MVI A, 34 H.

AU : Dec.-16

Ans. : Opcode fetch and memory read.