Microprocessors and its Applications Interview question and discussion

Real Time Systems are those in which timeliness is as important as the correctness of the outputs, although this does not mean that they have to be “fast systems”.

4. List the limitations of 8 bit microprocessor:

Lower Execution Speed

It can address less memory size

Few instructions are available

5. What do you mean ‘ Data Width’?

Data Width is the width of the ALU. An 8 bit ALU can add / subtract/ multiply etc.. two 8 bit numbers . In many cases, the external data bus is the same width as the ALU, but not always. The 8088 had a 16 bit ALU and 8 bit bus , while the modern Pentiums fetch data 64 bits at a time for their 32 bit ALUs.

6. Draw and specify the complete bit configuration of 8085 flag Register?

D7 D6 D5 D4 D3 D2 D1 D0

S- Sign Flag . If D7 =1 , then sign flag is set, otherwise rest.

Z-Zero flag. If ALU operation results in zero, then this flag is set, Otherwise it is reset.

AC-Auxilliary flag. In an arithmetic operation ,when a carry is generated by digit D3 and passed on to digit D4, the AC flag is set. Otherwise it is reset.

P-Parity Flag. If the result of an arithmetic or logic operation has an even number of 1’s then this flag is set. Otherwise it is reset.

CY-Carry Flag. If an arithmetic operation results in a carry, the carry flag is set. Otherwise it is reset.

7. What is compiler?

Compiler is a program that translates English like words of a high level language into the machine language of a computer. A compiler read a given program ,called a source code, in its entirely and then translates the program into the machine language, which is called an Object Code.

8. List the four operations commonly performed by MPU( Micro processing Unit)?

Memory Read : Reads data (or instructions) from memory.

Memory Write: Writes Data (or instructions) into memory.

I/O Read: Accepts data from input devices.

I/O Write: Sends data to output devices.

9. Write about RST pins in 8085?

In 8085 ,three RST pins are available, such as RST 7.5 ,RST 6.5 , RST 5.5

RST represents Restart Interrupts. These are vectored interrupts that transfer the program control to specific memory locations. They have higher priorities than the INTR interrupt. Among these three, the priority order is 7.5,6.5,5.5.

10. List the control and status signals available in 8085

_{----- ------ ----}

ALE , RD, WR, IO/M, S1, S2

ALE-Address Latch Enable

_-----

RD – Read Control Signal

----

WR – Write Control Signal

_---

IO/M - To specify I/O or memory operation

S1 , S2 – Status signals

11. What are the limitations of 8085 MPU?

(i) The lower order address bus of the 8085 microprocessor is multiplexed (time shared) with the data bus. The buses need to be demultiplexed.

(ii) Appropriate control signals need to be generated to interface memory and I/O with the 8085.

12. Compare the 8 bit microprocessors 8080A and 8085.

8080A is the predecessor of 8085. 8085 has the instruction set of 8080A plus some additional ones. Program written for 8080A will be executed by 8085. 8085 and 8080A are not pin compatible. Both require a +5V power supply.

13. Define Register Relative Addressing Mode.

Register Relative Addressing Mode : The Effective Address is Calculated by the sum of 8- or 16 bit displacement and the contents of a base Register or an index Register.

E.A. = content of(BX or BP or SI or DI) + (8 bit displacement (sign extended ) or 16 bit displacement

Physical Address = E.A +(DS)*16₁₀

14. Define Immediate Addressing.

An 8 bit or 16 bit immediate data follows the instruction. For e.g MOV AX,5020H instruction transfers a word 5020H to the AX register .

15. Define Direct Addressing mode :

A 16 bit offset address of the data memory location is specified with reference to the DS segment starting address.

For.E.g MOV [1020H],5020H instruction transfers a word 5020H to the data memory location at 11020H if DS=1000H.

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