Saturday, 26 May 2012


50 Common Interview Questions and Answers :

Review these typical interview questions and think about how you would answer them. Read the questions listed; you will also find some strategy suggestions with it.

1. Tell me about yourself:
The most often asked question in interviews. You need to have a short statement prepared in your mind. Be careful that it does not sound rehearsed. Limit it to work-related items unless instructed otherwise. Talk about things you have done and jobs you have held that relate to the position you are interviewing for. Start with the item farthest back and work up to the present.
2. Why did you leave your last job?
Stay positive regardless of the circumstances. Never refer to a major problem with management and never speak ill of supervisors, co- workers or the organization. If you do, you will be the one looking bad. Keep smiling and talk about leaving for a positive reason such as an opportunity, a chance to do something special or other forward- looking reasons.
3. What experience do you have in this field?
Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.

4. Do you consider yourself successful?
You should always answer yes and briefly explain why. A good explanation is that you have set goals, and you have met some and are on track to achieve the others. 
5. What do co-workers say about you?
Be prepared with a quote or two from co-workers. Either a specific statement or a paraphrase will work. Jill Clark, a co-worker at Smith Company, always said I was the hardest workers she had ever known. It is as powerful as Jill having said it at the interview herself.
6. What do you know about this organization?
This question is one reason to do some research on the organization before the interview. Find out where they have been and where they are going. What are the current issues and who are the major players?
7. What have you done to improve your knowledge in the last year?
Try to include improvement activities that relate to the job. A wide variety of activities can be mentioned as positive self-improvement. Have some good ones handy to mention.
8. Are you applying for other jobs?
Be honest but do not spend a lot of time in this area. Keep the focus on this job and what you can do for this organization. Anything else is a distraction.
9. Why do you want to work for this organization?
This may take some thought and certainly, should be based on the research you have done on the organization. Sincerity is extremely important here and will easily be sensed. Relate it to your long-term career goals.
10. Do you know anyone who works for us?
Be aware of the policy on relatives working for the organization. This can affect your answer even though they asked about friends not relatives. Be careful to mention a friend only if they are well thought of.
11. What kind of salary do you need?
A loaded question. A nasty little game that you will probably lose if you answer first. So, do not answer it. Instead, say something like, That's a tough question. Can you tell me the range for this position? In most cases, the interviewer, taken off guard, will tell you. If not, say that it can depend on the details of the job. Then give a wide range.
12. Are you a team player?
You are, of course, a team player. Be sure to have examples ready. Specifics that show you often perform for the good of the team rather than for yourself are good evidence of your team attitude. Do not brag, just say it in a matter-of-fact tone. This is a key point.
13. How long would you expect to work for us if hired?
Specifics here are not good. Something like this should work: I'd like it to be a long time. Or As long as we both feel I'm doing a good job.

14. Have you ever had to fire anyone? How did you feel about that?
This is serious. Do not make light of it or in any way seem like you like to fire people. At the same time, you will do it when it is the right thing to do. When it comes to the organization versus the individual who has created a harmful situation, you will protect the organization. Remember firing is not the same as layoff or reduction in force. 

15. What is your philosophy towards work?
The interviewer is not looking for a long or flowery dissertation here. Do you have strong feelings that the job gets done? Yes. That's the type of answer that works best here. Short and positive, showing a benefit to the organization.
16. If you had enough money to retire right now, would you?
Answer yes if you would. But since you need to work, this is the type of work you prefer. Do not say yes if you do not mean it.
17. Have you ever been asked to leave a position?
If you have not, say no. If you have, be honest, brief and avoid saying negative things about the people or organization involved.

18. Explain how you would be an asset to this organization.
You should be anxious for this question. It gives you a chance to highlight your best points as they relate to the position being discussed. Give a little advance thought to this relationship.
19. Why should we hire you?
Point out how your assets meet what the organization needs. Do not mention any other candidates to make a comparison.

20. Tell me about a suggestion you have made.
Have a good one ready. Be sure and use a suggestion that was accepted and was then considered successful. One related to the type of work applied for is a real plus.
21. What irritates you about co-workers?
This is a trap question. Think real hard but fail to come up with anything that irritates you. A short statement that you seem to get along with folks is great.

22. What is your greatest strength?
Numerous answers are good, just stay positive. A few good examples: Your ability to prioritize, Your problem-solving skills, Your ability to work under pressure, Your ability to focus on projects, Your professional expertise, Your leadership skills, Your positive attitude
23. Tell me about your dream job.
Stay away from a specific job. You cannot win. If you say the job you are contending for is it, you strain credibility. If you say another job is it, you plant the suspicion that you will be dissatisfied with this position if hired. The best is to stay genetic and say something like: A job where I love the work, like the people, can contribute and can't wait to get to work.
24. Why do you think you would do well at this job?
Give several reasons and include skills, experience and interest.

25. What are you looking for in a job?
See answer # 23
26. What kind of person would you refuse to work with?
Do not be trivial. It would take disloyalty to the organization, violence or lawbreaking to get you to object. Minor objections will label you as a whiner. 

27. What is more important to you: the money or the work?
Money is always important, but the work is the most important. There is no better answer.

28. What would your previous supervisor say your strongest point is?
There are numerous good possibilities: 
Loyalty, Energy, Positive attitude, Leadership, Team player, Expertise, Initiative, Patience, Hard work, Creativity, Problem solver

29. Tell me about a problem you had with a supervisor.
Biggest trap of all. This is a test to see if you will speak ill of your boss. If you fall for it and tell about a problem with a former boss, you may well below the interview right there. Stay positive and develop a poor memory about any trouble with a supervisor.
30. What has disappointed you about a job?
Don't get trivial or negative. Safe areas are few but can include:
Not enough of a challenge. You were laid off in a reduction Company did not win a contract, which would have given you more responsibility.

31. Tell me about your ability to work under pressure.
You may say that you thrive under certain types of pressure. Give an example that relates to the type of position applied for.

32. Do your skills match this job or another job more closely?
Probably this one. Do not give fuel to the suspicion that you may want another job more than this one.

33. What motivates you to do your best on the job?
This is a personal trait that only you can say, but good examples are: Challenge, Achievement, Recognition

34. Are you willing to work overtime? Nights? Weekends?
This is up to you. Be totally honest.

35. How would you know you were successful on this job?
Several ways are good measures:
You set high standards for yourself and meet them. Your outcomes are a success.Your boss tell you that you are successful

36. Would you be willing to relocate if required?
You should be clear on this with your family prior to the interview if you think there is a chance it may come up. Do not say yes just to get the job if the real answer is no. This can create a lot of problems later on in your career. Be honest at this point and save yourself uture grief.
37. Are you willing to put the interests of the organization ahead of your own?
This is a straight loyalty and dedication question. Do not worry about the deep ethical and philosophical implications. Just say yes.

38. Describe your management style.
Try to avoid labels. Some of the more common labels, like progressive, salesman or consensus, can have several meanings or descriptions depending on which management expert you listen to. The situational style is safe, because it says you will manage according to the situation, instead of one size fits all.
39. What have you learned from mistakes on the job?
Here you have to come up with something or you strain credibility. Make it small, well intentioned mistake with a positive lesson learned. An example would be working too far ahead of colleagues on a project and thus throwing coordination off.
40. Do you have any blind spots?
Trick question. If you know about blind spots, they are no longer blind spots. Do not reveal any personal areas of concern here. Let them do their own discovery on your bad points. Do not hand it to them.
41. If you were hiring a person for this job, what would you look for?
Be careful to mention traits that are needed and that you have.

42. Do you think you are overqualified for this position?
Regardless of your qualifications, state that you are very well qualified for the position.

43. How do you propose to compensate for your lack of experience?
First, if you have experience that the interviewer does not know about, bring that up: Then, point out (if true) that you are a hard working quick learner.

44. What qualities do you look for in a boss?
Be generic and positive. Safe qualities are knowledgeable, a sense of humor, fair, loyal to subordinates and holder of high standards. All bosses think they have these traits.
45. Tell me about a time when you helped resolve a dispute between others.
Pick a specific incident. Concentrate on your problem solving technique and not the dispute you settled.

46. What position do you prefer on a team working on a project?
Be honest. If you are comfortable in different roles, point that out.

47. Describe your work ethic.
Emphasize benefits to the organization. Things like, determination to get the job done and work hard but enjoy your work are good.

48. What has been your biggest professional disappointment?
Be sure that you refer to something that was beyond your control. Show acceptance and no negative feelings.

49. Tell me about the most fun you have had on the job.
Talk about having fun by accomplishing something for the organization.

50. Do you have any questions for me?
Always have some questions prepared. Questions prepared where you will be an asset to the organization are good. How soon will I be able to be productive? and What type of projects will I be able to assist on? are examples.
And Finally Good Luck

Monday, 13 February 2012

Interview Tips For Freshers........


1.       Try to appear your best at the Interview.  Your appearance should convey that you have taken the interview seriously.   Do not try to turn up in the interview in a manner that does not suit you.   Some basics in grooming will help.
a.       Well Groomed Hair
b.      Well Pressed Shirt
c.       Polished Shoes

2.       Know about the company.   You should learn as much as you can about the company.  A good place to start is the company's website.  If you have been referred through a friend also have a frank discussion with him or her.  Also, do a google search  on the company to understand what others are saying about the company.

3.       Answer clearly and directly.  Spell out your ideas as clearly as you can.  Also try to substantiate your ideas with examples.  Don't be overly wordy and try to keep your answers to the point.  Do not try to deviate too much from the question.

4.       Do not be argumentative.  Present your viewpoint and be professional.  If you do not agree with something the Interviewer has said do not spurn it as invalid.  Learn to understand their point of view even if it clashed with your own.  This does not mean that you need to accept their point of view.

5.       Be prepared with questions for the Interviewer.  Most interviewers will give you a chance to ask questions.  Use this opportunity to show your knowledge and interest in the company.  Also this is a good opportunity to clear any doubts that you have.

6.       Address the Interviewer politely.  It is always polite to refer to the Interviewer as SIR or Maam.  You can also address them their Surname (Mr. XXX or Mrs. XXX).  Do not use terms such as Honey, Girl, Dude, Yaar etc.

7.       Be Confident.  Be confident, you have prepared well and this should show in your confidence level in the interview.

Thursday, 2 February 2012

8086 Instruction Set


8086 Instruction Set Summary


Data Transfer Instructions

MOV Move byte or word to register or memory
IN, OUT Input byte or word from port, output word to port
LEA Load effective address
LDS, LES Load pointer using data segment, extra segment
PUSH, POP Push word onto stack, pop word off stack
XCHG Exchange byte or word
XLAT Translate byte using look-up table
Logical Instructions
NOT Logical NOT of byte or word (one's complement)
AND Logical AND of byte or word
OR Logical OR of byte or word
XOR Logical exclusive-OR of byte or word
TEST Test byte or word (AND without storing)
Shift and Rotate Instructions
SHL, SHR Logical shift left, right byte or word? by 1 or CL
SAL, SAR Arithmetic shift left, right byte or word? by 1 or CL
ROL, ROR Rotate left, right byte or word? by 1 or CL
RCL, RCR Rotate left, right through carry byte or word? by 1 or CL



Arithmetic Instructions


ADD, SUB Add, subtract byte or word
ADC, SBB Add, subtract byte or word and carry (borrow)
INC, DEC Increment, decrement byte or word
NEG Negate byte or word (two's complement)
CMP Compare byte or word (subtract without storing)
MUL, DIV Multiply, divide byte or word (unsigned)
IMUL, IDIV Integer multiply, divide byte or word (signed)
CBW, CWD Convert byte to word, word to double word (useful before multiply/divide)

AAA, AAS, AAM,
AAD
ASCII adjust for addition, subtraction, multiplication, division (ASCII
codes 30-39)
DAA, DAS Decimal adjust for addition, subtraction (binary coded decimal numbers)


Conditional jumps:


JA (JNBE) Jump if above (not below or equal)? +127, -128 range only
JAE (JNB) Jump if above or equal(not below)? +127, -128 range only
JB (JNAE) Jump if below (not above or equal)? +127, -128 range only
JBE (JNA) Jump if below or equal (not above)? +127, -128 range only
JE (JZ) Jump if equal (zero)? +127, -128 range only
JG (JNLE) Jump if greater (not less or equal)? +127, -128 range only
JGE (JNL) Jump if greater or equal (not less)? +127, -128 range only
JL (JNGE) Jump if less (not greater nor equal)? +127, -128 range only
JLE (JNG) Jump if less or equal (not greater)? +127, -128 range only
JC, JNC Jump if carry set, carry not set? +127, -128 range only
JO, JNO Jump if overflow, no overflow? +127, -128 range only
JS, JNS Jump if sign, no sign? +127, -128 range only
JNP (JPO) Jump if no parity (parity odd)? +127, -128 range only
JP (JPE) Jump if parity (parity even)? +127, -128 range only


Loop control:


LOOP Loop unconditional, count in CX, short jump to target address
LOOPE (LOOPZ) Loop if equal (zero), count in CX, short jump to target address
LOOPNE (LOOPNZ) Loop if not equal (not zero), count in CX, short jump to target address
JCXZ Jump if CX equals zero (used to skip code in loop)


Subroutine and Interrupt Instructions


CALL, RET Call, return from procedure (inside or outside current segment)
INT, INTO Software interrupt, interrupt if overflow
IRET Return from interrupt

String Instructions


MOVS Move byte or word string
MOVSB, MOVSW Move byte, word string
CMPS Compare byte or word string
SCAS Scan byte or word string (comparing to A or AX)
LODS, STOS Load, store byte or word string to AL or AX
Repeat instructions (placed in front of other string operations):
REP Repeat
REPE, REPZ Repeat while equal, zero
REPNE, REPNZ Repeat while not equal (zero)

Processor Control Instructions
Flag manipulation:

STC, CLC, CMC Set, clear, complement carry flag
STD, CLD Set, clear direction flag
STI, CLI Set, clear interrupt enable flag
LAHF, SAHF Load AH from flags, store AH into flags
PUSHF, POPF Push flags onto stack, pop flags off stack

Coprocessor, multiprocessor interface:

ESC Escape to external processor interface
LOCK Lock bus during next instruction

Inactive states:

NOP No operation
WAIT Wait for TEST pin activity
HLT Halt processor






Saturday, 29 October 2011

Microprocessor(8085/8086) Question bank


Question Bank
Microprocessor and its Application (EC-307)
B.Tech, 5th Semester ECE
Introduction to Microprocessor
Marks: 2 each
1. List the components of a computer
2. Explain the function of each component of a computer.
3. What is a Microprocessor? What is the difference between a Microprocessor & CPU?
4. Define bit, byte, word, double word, quad word and instruction
5. What determines that Microprocessor is an 8, 16 or 32 bit?
6. Explain the difference between the machine language and the assembly language of
the 8085 microprocessor.
7. What is an assembler?
8. What are low and high level languages?
9. What are the advantages of an assembly language in comparison with high level
languages?
10. List the four operations commonly performed by the MPU.
11. Specify the four control signals commonly used by the 8085 MPU.
12. Specify the function of the address bus and the direction of the information flow on
the address bus.
13. Why is the data bus bidirectional?
14. What is a bus?
8085 Microprocessor
Marks: 2 each
15. How many memory locations can be addressed by a microprocessor with 14 address
lines?
16. How many address lines are necessary to address two megabytes (2048K) of
memory?
17. Why is the data bus bidirectional?
18. Specify the control signal and the direction of the data flow on the data bus in a
memory-write operation.
19. What is the function of the accumulator?
20. What is a flag?
21. Why are the program counter and the stack pointer 16-bit registers?
22. What is the function of the WR signal on the memory chip?
23. Specify the number of registers and memory cells in a 128 x 4 memory chip.
24. What is the memory word size required in an 8085 system?
25. While executing a program, when the 8085 MPU completes the fetching of the
machine code located at the memory address 2057H, what is the content of the
program counter?
26. What is the role of clock in Microprocessor?

Marks: 5 each
27. What is the difference between INR & INX instructions?
28. List all the interrupt signals of 8085 microprocessor.
29. Write short note on evolution of microprocessors.
30. Explain the functions of the ALE and IO/M signals of the 8085 microprocessor.
31. List the sequence of events that occurs when the 8085 MPU reads from memory.
32. If the 8085 adds 87H and 79H, specify the contents of the accumulator and the status
of the S, Z, and CY flags.
33. If the clock frequency is 5 MHz, how much time is required to execute an instruction
of 18 T-states?
34. Discuss the programming model of 8085 μP with the help of suitable diagram.
35. Draw and explain the timing diagram for opcode fetch operation
36. Discuss various types of addressing modes of 8085.
37. Explain why the number of output ports in the peripheral-mapped I/O is restricted to
256 ports.
38. In the peripheral-mapped I/O, can an input port and an output port have the same port
address? Explain.
39. What are the control signals necessary in the memory-mapped I/O?
40. List the four categories of 8085 instructions that manipulate data.
41. Define opcode and operand, and specify the opcode and the operand in the instruction
MOV H, L.
42. Write logical steps to add the following two Hex numbers. Both the numbers should
be saved for future use. Save the sum in the accumulator. Numbers:
A2H and 18H.
Marks: 10 each
43. (a)Specify the contents of the registers and the flag status as the following
instructions are executed.
i. MVI A, 00H
ii. MVI B, F8H
iii. MOV C, A
iv. MOV D, B
v. HLT
(b)Write instructions to load the hexadecimal number 65H in register C and 92H in
accumulator A. Display the number 65H at PORT0 and 92H at PORT1.
44. Draw and explain the block diagram of a microprocessor 8085.
45. (a)Why the lower order address bus is multiplexed with data bus? How they will be
de-multiplexed?
(b) Differentiate between maskable and non-maskable interrupts.
46. Write an 8085 assembly language program using minimum number of instructions to
add the 16 bit no. in BC, DE & HL. Store the 16 bit result in DE pair.
47. (a)Explain in detail the following instructions:-
(i) ADC (ii) LHLD (iii) RLC (iv) DI
(b) Define & explain the term addressing modes.
8086 Microprocessor
Marks: 2 each
48. What are important signals of Intel 8086?
49. How many operating modes does 8086 have?
50. How many functional units does 8086 contain?
51. What is the function of a segment register in 8086?
52. What are conditional and control flags in 8086?
53. How many interrupt lines does 8086 have?
54. What physical address is represented by:
(i) 4370 : 561E H (ii) 7A32 : 0028 H
55. Describe the difference between the instructions:
(i) MOV AL, 0DB H (ii) MOV AL,DB H
Marks: 5 each
56. Briefly explain the maximum mode configuration of 8086.
57. What is the difference between minimum and maximum modes of 8086?
58. How many interrupts are available in 8086? List the predefined software interrupts
available in 8086.
59. Briefly explain the maximum mode configuration of 8086.
60. What is the purpose of MN/Mx pin? Explain.
61. Explain the concept of segmented memory? What are its advantages?
62. Explain the concept of pipelining in 8086. Discuss its advantages and disadvantages.
Marks: 10 each
63. Discuss the interrupt system of Intel 8086. What is interrupt pointer? What is 'type' of
an interrupt?
64. Discuss the various addressing modes of 8086. What are displacement, base and
index? What is an effective address or offset?
65. What is the difference between minimum and maximum modes of 8086? How are
these modes selected?
66. Draw and explain the architecture of 8086.
67. Write an 8086 program to add two 16-bit numbers in CX and DX and store the result
in location 0500H addressed by DI.
Microprocessor system peripheral and interface
Marks: 5 each
68. What is interfacing?
69. Explain the concept of Direct Memory Access (DMA).
70. Explain the functions of Handshake signals.
71. Explain what SIM is. Discuss the bit pattern of the accumulator for SIM instruction.
72. List the operating modes of the 8155A programmable device.
73. Write a note on any of the applications of microprocessors.
Marks: 10 each
74. Explain the DMA controller 8257?
75. Draw the block diagram of 8255 and explain its working. What is Control Word?
Determine the control word for the following configuration of 8255:-
Port A – Output
Mode of port A – Mode 1
Port B – Output
Mode of port B – Mode 0
Port C lower (pins PC0 – PC2) – Output
76. What is 8254? Discuss its various operating modes. What are its areas of
applications?
77. Explain major components of 8259 with the aid of suitable diagram.
78. Explain USART in detail.
79. Explain the functional diagram of keyboard and display controller.
80. Explain the functional diagram of 8155 and explain its control word.

8086 Microprocessor


Introduction:
8086 microprocessor is introduced in 1978 by intel co. and adopted by IMB for their PC in 1981. The intel 8086 is 16 bit, N-channel, HMOS(High speed - MOS) microprocessor, It consumes less power and draws 360mA current on 5V supply.8086 is manufactured for standard temperature range 32F to 180F as well as extended temp. range 40F to 225F. In market 3 version of 8086 are available
S. No.
Version
Frequency
1.
8086
5 Mhz
2.
8086-1
10 Mhz
3.
8086-2
8 Mhz

It is built on a single-semiconductor chip and packed in 40 pin IC pack, the package is DIP (Dual In-Line Package).It contains an electronic circuit of 29000 transistors. 8086 is the first member of X86 or 80X86 family followed by 8088, 80186, 80188, 80386, 80486 and Pentium names.
Features of 8086 microprocessor:
1.      It is 16 bit microprocessor.
2.      It has 20 address lines, so it can address 220 = 1mb memory locations.
3.      It has multiplexed address and data bus which reduced the no. Of pins needed, but multiplexing slightly slow down the transition of data.
4.      It has 16 control lines for providing handshaking singles during bus transfer and for permitting at least some external control of the CPU.
5.      It requires only one, +5 volt supply voltage.
6.      It supports both multiprogramming and multiprocessing.
7.      Its instruction stream byte queue speed up its execution of instruction.
Pin Description of 8086:
AD0-AD15: (Bidirectional) Address/data lines, these are low order address bus and multiplexed with data.
AD16-AD20: High order address bus multiplexed with status signals.
AD16/S3,AD17/S4: AD16 & AD17 multiplexed with segment identifier signals S3 & S4,
AD18/S5:  AD18 is multiplexed with interrupt status S5,
AD19/S6: AD19 is multiplexed with status signal S6.
BHE /S7 (output): Bus high enable/ status. It is used to enable data onto the most significant half of data bus, D8-D15, 8bit device connected to upper half of the bus use BHE signal. It is multiplexed with status S7.
RD(read) : Signal is used to read operation. It is an output signal and active when low. READY (Input) : The addressed I/O or memory sends acknowledgement through this pin. When high it indicates that the peripheral is ready to transfer.
RESET (Input) :  System is reset. The signal is Active high.
CLK (input) : Clock 5,10 or 8 MHz
INTR(Interrupt Request):
QS1
QS0
OPERATION
0
0
     No operation
0
1
     1st byte of opcode from queue
1
0
     Empty the Queue
1
1
     Subsequent byte from Queue







NMI (Input): Non maskable interrupt request.
TEST (Input) : Wait for test control. When it is low the microprocessor continues execution otherwise wait.
S0, S1, S2 (OUTPUT): Pin no. 26,27,28. Status signals. These signals are connected to the bus controller Intel 8288.The bus controller generates memory and I/O access control signal.
S0
S1
S2
Operation
0
0
0
Interrupt acknowledge.
0
0
1
Read data form I/O port.
0
1
0
Write Data to I/O port.
0
1
1
Halt.
1
0
0
Opcode fetch.
1
0
1
Memory Read.
1
1
0
Memory Write.
1
1
1
Passive state.

LOCK (Output) : Active Low, All interrupts are masked and no hold request is granted.
RQ/GT1 , RQ/GT0 : (Bidirectional) Local bus priority control, other bus ask CPU through these lines to release the local bus.(RQ/GT0 has higher priority than RQ/GT1)
Vcc : Power Supply.                          GND: Ground
Operating modes of 8086:
1.      Minimum Operating Mode:  In this mode 8086 works only as CPU of the System.
2.      Maximum Operating Mode: In this mode issue of I/O peripheral and Memory is included.
Block Diagram of 8086:

BUS Interface Unit (BUI): BUI provides an interface of 8086 microprocessor to the outside world. The BUI is responsible for performing all external bus operations. It provides a 16-bits Bidirectional data bus and 20 bits unidirectional address bus.
Roles of BUI:
1.      It sends out address.
2.      Fetches instruction from memory.
3.      Reads data from the ports and memory.
4.      Write data to ports and memory.
Execution Unit (EU): EU contains control circuitry of the microprocessor and translates the instruction fetched from the memory into a series of actions. The 16 bit ALU of execution unit carries out addition, subtraction, AND, OR, XOR, increment, decrement, complement of the binary numbers.
Instruction Stream Byte Queue:  It is also named as instruction Queue or The Queue. This Queue is a set of 6 registers each can store one byte. While EU decodes and executes the instruction then it does not uses buses, in this time BUI fetches upto six instructions and store these prefetched instruction in this FIFO register set. When EU Ready for next instruction it simply reads the prefetched instruction from the Queue. This is much faster than getting instruction from the memory. But in case of JUMP and CALL instruction Queue must be dumped and reloaded stating from new address.
Note: The process of Fetching next instruction while current instruction executes is called pipelining.
Sequential Memory Organization: 8086 microprocessor has 220 = 1,048,576 = 1 Mb locations. Each having 1,048,576 addresses represents a byte wide locations, A 16-bit word will be stored in two consecutive locations. If the 1st word has even address, 8086 can read entire word in one operation and if address is odd then 8086 reads 1st byte with one bus operation another with 2nd bus operation.
MEMORY SEGMENTS: Memory of 8086 is divided into 4 segments each of 64kb within the 1Mb memory space. Each segment represents 64kb consecutive memory location.
Each Segment is assigned a base address that identifies the starting address of the segment.
SEGMENTS ARE:
1.      CODE SEGMENT(CS)
2.      DATA SEGMENT(DS)
3.      EXTRA SEGMENT(ES)
4.      STACK SEGMENT(SS)
Merits of Memory Segmentation :
1.      It facilitates the separate memory area for a program, its data, and the stack.
2.       It facilitates the Multiprogramming and multitasking.
3.      It permits a program and/or its data to be put into different areas of memory each time the program is executed.
4.      Memory capacity becomes 1 mB even through the addres associated with the individual instruction are only 16 bit long.
Registers of 8086:
1.      General Purpose Register (GPR): There are 4 16 bit GPR ( AX, BX, CX, DX) further divided into two 8 bit register.
16 bit Register
8 bit High Order Register
8 bit Low Order Register
AX
AH
AL
BX
BH
BL
CX
CH
CL
DX
DH
DL

2.      Pointer and Index Register: There are two pointer and two index register in 8086.
a.      Stack Pointer (SP)
b.      Base Pointer (BP)
c.      Source Index (SI)
d.      Destination Index (DI)
3.      Segment Registers( CS, DS, ES, SS)
4.      Instruction pointer: It is a 16 bit register and identifies the address of the next instruction to be executed in the code segment. 16 bit content of the IP is called offset or Effective Address (EA).

      Physical Address (PA) = Effective Address (EA) + Code segment (CS)


5.      Status Flag( There are 9 flag register in 8086)



Classification of 8086 Instructions
1.      Data Transfer Instruction: Move, load, store, exchange, input, output, push, and pop are data transfer instruction. For these instructions source and destination may be register, memory and port. e.g.: MOV, XCHG, POP, PUSH etc.
2.      Arithmetic Instruction: Instruction of this group perform addition, subtraction, multiplication division, increment, decrement, comparison, ASCII and decimal adjustment etc. E.g.: ADD, SUB, MUL, DIV, CMP etc.
3.      Logical Instruction: These instructions perform logical operations. E.g.: AND, OR, XOR, NOT and TEST operation. Rotate and shift operation may be included in this group.
4.      Program Execution Transfer (Branch) Instruction: Instruction of this group transfer program execution from the normal sequence to specific destination or target. After the execution of such instruction process start fetching instruction from some new address, rather than continuing same address. E.g. : JMP,JA(JUMP if Above), JAE(JUMP if above or equal),JB(JUMP if Below) JBE, JC, JNC, JNB(JUMP if not Below), JNA etc.
a.      Iteration Control Instruction: Such as LOOP, LOOPE, LOOPZ, LOOPNE, LOOPNZ etc may be included in this group.
b.      Interrupt Instruction: such as INT (Software Interrupt), INTO (Interrupt on Overflow) and IRET (Return form Interrupt Service Subroutine) can also include in this group.
c.      Processor Control Instruction: Instructions of this group are related to flag manipulation and machine control. Example: CLC (Clear Carry Flag), CLD (Clear Direction Flag), CLI (Clear Interrupt Flag) etc.
Addressing Modes of 8086:
There are 8 addressing modes in 8086
Ø      Register Addressing: Operand is placed in a 16 bit or 8 bit register.
                        E.g. : a. MOV AX,BX
                                    b. ADD AL,BL
Ø      Immediate Addressing:  Operand is specified in the instruction itself.
                        E.g.:     a. MOV AL,35H
                                    b. ADD BX,0102H
Ø      Direct Addressing: Operands Offset is given in the instruction itself.
                        E.g.:     a. ADD AL,[0310]
                                    b. ADD AX,[0310]
Ø      Register Indirect Addressing: Operands Offset is placed in any register(BX,BP or SI) specified in the instruction.
                        E.g.:     a. MOV AX,[BX]
                                    b. ADD AL,[SI]
Ø      Based Addressing: Offset of Operand is sum of the content of BX or BP with 8 bit or 16 bit displacement.
            Offset( E.A.) = [ BX + 8 bit or 16 bit Displacement]
                        E.g.:     a. MOV AL,[BX+05]
                                    b. MOV AL,[BX+1346H]
Ø      Index Addressing: Operand’s Offset is sum of content of Index Register(SI or DI) and 8bit or 16 bit displacement.
                        Offset =[SI or DI + 8 bit or 16 bit displacement]
                        E.g.:     a. ADD AX,[SI+05]
                                    b. MOV BX,[DI+1523H]
Ø      Based Indexed Addressing: Offset of operand is sum of Base Register and Index register .
            Offset = [BX or BP] +[SI or DI]
                        E.g.      a. ADD AX,[BX+SI]
                                    b. MOV CX,[BX+SI]
Ø       Based Indexed with Displacement : Offset is given as follows
            Offset = [BP or BX] + [SI or DI] + 8 bit or 16 bit Displacement
                        E.g.:     a. MOV AX,[BX+SI+05]
                                    b. ADD AX,[BX+SI+1234H]