Microprocessor Interview Questions & Answers

Question 1. Describe Briefly Any Three Types Of Transmission?

Answer :

The various types of commonly used transmissions are as follows:

Simplex Transmission: This type of data transmission involves data to be moved only in one direction. In this no data can be sent back using the same channel. A  good example of this form of transmission can be found in a keyboard.

Half Duplex Transmission: This type of transmission allows data to be transferred in both directions but not at the same time. One end transmits while the other  receives.

Full Duplex Transmission: In this type of transmission data can be sent and received at the same time. There are no two different modes such as transmit and  receive.

Question 2. Briefly Explain The 8279 Operation ?

Answer :

• The 8279 is basically a programmable keyboard and a component for display interfacing.
• The 8279 can scan and also encode a 64 key keyboard as well as a numerical display of 16 digits.
• The keyboard has a buffer based on FIFO to store up to 8 keys after which the processor must retrieve a character.
• It contains 8 lines that can be used to connect to 8 columns of a keyboard. There are two additional lines for STB keys.
• Once a key is pressed they are automatically debounced and it can function using two modes -key lockout and n-key roller.
• On simultaneous presses only the first key is detected. In case of n-key rollover mode all simultaneous presses are detected and stored in the internal buffer.

Question 3. Briefly Mention The Differences Between Vga And Cga Graphics.?

Answer :

The characteristics of CGA are as follows:

• The CGA or the Color/Graphics adapter was the first color graphics card for IBM pc`s.
• It contain 16KB of video memory and used an Rca jack to connect to a Tv or monitor ( NTSC compatible).
• It could also be connected to a RBGI interface CRT monitor (4-bit).
• The characteristics of VGA graphics are as follows:
• The VGA or the video graphics array was a hardware introduced with the IMB PS/2 computers.
• It has been widely adopted world over and now actually implies the analog computer display standard.
• Eventually after much modifications by other manufacturers the VGA was superseded by SVGA.

Question 4. Describe Briefly The External And Internal Bus Of The 8088 Processor?

Answer :

• Internal Data Bus: As its name suggests the internal data bus only works inside a CPU that is internally. It is able to communicate with the internal cache memories of  the CPU. Since they are internally placed they are relatively quick and are now affected by the rest of the computer.
• External Data bus: This type of bus is used to connect and interface the computer to its connected peripheral devices. Since they are external and do not lie within the circuitry of the cpu they are relatively slower.
• The 8088 processor in itself contains a 16-bit internal data bus coupled with a 20-bit address register. This allows the processor to address to a maximum of 1 MB.

Question 5. Explain Briefly The Role Of The 8284 Processor?

Answer :

• The 8284 is considered to be a supporting part for microprocessors. It is responsible for the generation of clock signals.
• The clock generator forms an intrinsic part of a circuit as without it every component in the system would have to create a signal for it independently.
• When F/C’ is at logic, the oscillator output is steered through to the divide-by-3 counter.

Question 6. How Can A Microprocessor Based Computer System Be Developed?

Answer :

In developing a Microprocessor based computer system the following steps are involved: 

1. The first step is to develop the CPU module.By doing so the basic system timing, sequential startup order is established. 
2. After that memory needs to be added: The primary memory is essential for the programs that are stored on the computer. There can be several forms of memories with different hierarchies. The CPU loads and fetches instruction from the memory.
3. The third step is adding input/output: There are basically two hardware techniques for getting data into and out of a computer. 

1. The parallel interface is the most common and natural form. 
2. The serial interface is the second technique.

Question 7. Explain In Pentium Processors How Memory Management Has Been Improved?

Answer :

• By adding a paging unit and a new system in the memory system the management of it has been improved upon.
• Paging Unit: The paging mechanism works on 4KB memory pages or with a  new extension available to the Pentium with 4MB memory pages. 
• Memory-management mode: The system memory-management mode (SMM) is on the equal levels such as the protected mode, real mode, and virtual mode. Still the memory management mode function as a manager. High-level system functions  such as power management and security are taken care of by it.

Question 8. What Do You Understand By Macro? Explain The Various Conditional Constructs Used While Programming A Macro?

Answer :

• Macro can be considered to be a sequence of instructions to which a name is assigned.
• For short sequence of instructions which are of fixed nature Macros are used.
• They can execute faster as compared to subroutines. 
• The MACRO directives are used to inform the assembler the starting of a macro.
• In order to enclose a macro the ENDM directive is used. 
• The general format of the MACRO directive is: Macro Name MACRO ARG1, ARG2 , …..,ARG N.
• To create macro sequences conditional assembly language statements are used. Theses statements control the flow of the program and are variations of the IF-THEN, IF-THEN-ELSE, DO-WHILE, and REPEAT-UNTIL constructs used in high-level language programming languages.

Question 9. Briefly Explain Cwd Instructions In 8086 Family?

Answer :

CWD also known as the Convert signed Word to signed Double word instruction, it is used to extend the sign bit of a word in AX register to all the bits of the DX register. Generally used before a signed word in AX. Then it is divided by another signed word using IDIV instruction. It does not affect any flag.

Question 10. Briefly Explain Loop Instructions In 8086 Family:

Answer :

LOOP: (Jump to specified label until CX = 0): As the name suggests the loop instruction is used to repeat a sequence of instructions for a specified number of time. It does not affect any flag and the number of times the loop is to be repeated is stored in the CX register.

Question 11. Briefly Explain Imul Instructions In 8086 Family?

Answer :

IMUL: This instruction is used for the multiplication of two signed numbers.The result of imul between two signed numbers is signed as well. The OF (Over flow) and CF (Carry flag) flags get affected by this instruction.

Question 12. Briefly Explain Sar Instructions In 8086 Family?

Answer :

SAR: Also known as Shift each bit of operand right, this instruction shifts each bit of the operand in a register or memory location, right by the number of bits specified. The carry flag is affected by this operation.

Question 13. Explain Segments Their Pro`s And A Method For Their Implementation?

Answer :

• The division of address space into logical sections is known as segmentation and each such space is known as a segment. 
• In order to access a specific memory location, a program must specify both the segment number and the offset contained in that segment. Segment memory addressing divides the memory into many segments. 
• One of the advantages of memory segmentation is that only 16 bit registers are  required to both store segment base address as well as offset address. Due to this the designing of the memory is simple.
• By using segmentation there is the advantage of relocability as well.

Question 14. Briefly Explain Dma And Its Various Addressing Modes?

Answer :

• The DMA or the direct memory access is a type of process in which the System bus control is accessed and controlled by an external device in place of the CPU.
• It is primarily used for the high speed transfer of data from mass storage devices.
• The DMA functions by directly transferring data to and from from the memory to the devices.
• The various modes of operation of the DMA are as follows: Demand mode, Single mode, Block mode and Cascade mode.
• The characteristic of the demand mode is that it can transfer data until the Dreq input becomes inactive.

Question 15. Briefly Explain The Functions Of Debugger, Assembler And The Linker?

Answer :

• Debugger: As its name suggests the debugger is used to test and debug programs. The debugger allows a user to test a program step by step, so that the problem points or steps can be identified and rectified. It allows the user to inspect the registers and the memory locations after a program has executed.
• Assembler: The assembler is used to convert assembly language written by a user or a program into a machine recognizable format.
• Linker: There are certain programs which are large in size and cannot be executed at one go simultaneously. Such programs are divided into subprograms also known as modules. The linker is used to link such small programs to form one large program.

Question 16. In Assembly Language, Write The Program To Search For The Largest Number Among N Numbers Which Are Stored In The Memory?

Answer :

The program to detect the largest number among n numbers stored in the memory are as follows:

Step 1>>MOV AX, 0000 

Step 2>>MOV SI, 0200 

Step 3>>MOV CX, [SI] 

Step 4>>BACK : INC SI 

Step 5>>INC SI 

Step 6>>CMP AX, [SI] 

Step 7>>JAE GO 

Step 8>>MOV AX, [SI] 

Step 9>>GO: LOOP BACK 

Step 10>>MOV [0251], AX 

Step 11>>INT 3

Question 17. Write A Program In Assembly Language To Find Out One`s And Two`s Complement For An 8 Bit Number?

Answer :

The program to find the one`s complement of an eight bit number is as follows:

LDA 2501H 

CMA 

STA 2502H 

HLT

The program to find the two`s complement is as follows:

LDA 2501H 

CMA 

INR A 

STA 2502H 

HLT