Important Short Questions and Answers: 8086 Microprocessor

THE 8086 MICROPROCESSOR

1. What is microprocessor?

A microprocessor is a multipurpose, programmable, clock-driven , register-based electronic device that reads binary information from a storage device called memory, accepts binary data as input and processes data according to those instructions, and provides result as output.

2. What is Accumulator?

The Accumulator is an 8-bit register that is part of the arithmetic/logic unit (ALU). This register is used to store 8-bit data and to perform arithmetic and logical operations. The result of an operation is stored in the accumulator. The accumulator is also identified as register A.

3. What is stack?

The stack is a group of memory locations in the R/W memory that is used for temporary storage of binary information during the execution of a program

4. What is a subroutine program?

A subroutine is a group of instructions written separately from the main program to perform a function that occurs repeatedly in the main program. Thus subroutines avoid the repetition of same set of instructions in the main program.

5. Define addressing mode.

Addressing mode is used to specify the way in which the address of the operand is specified within the instruction.

6. Define instruction cycle.

It is defined as the time required to complete the execution of an instruction.

7 . Write a program to add a data byte located at offset 0500H in 2000H segment to another data byte available at 0600H in the same segment and store the result at 0700H in the same segment.

MOV AX, 2000H; initialize DS with value MOVDS, AX; 2000H

MOV AX, [500H]; Get first data byte from 0500H offset ADD AX, [600H]; Add this to the second byte from 0600H MOV [700H],AX; store AX in 0700H

HLT; Stop.

8. What are the different types of addressing modes of 8086 instruction set? The different addressing modes are:

i. Immediate

ii. Direct

iii. Register

iv.Register indirect

v. Indexed

vi.Register relative

vii.Based indexed

viii.         Relative based indexed

9. What are the different types of instructions in 8086 microprocessor? The different types of instructions in 8086 microprocessor are:

i. Data copy / transfer instructions

ii. Arithmetic and logical instructions

iii. Branch instructions

iv.Loop instruction

v. Machine control instruction

vi.Flag manipulation instruction

vii.Shift and rotate instruction

viii.         String instruction

10.            What is assembly level programming?

A program called assembler is used to convert the mnemonics of instruction and data into their equivalent object code modules. The object code modules are further converted into executable code using linker and loader programs. This type of programming is called assembly level programming.

11. What is a stack?

Stack is a top-down data structure, whose elements are accessed using a pointer that is implemented using the SS and SP registers. It is a LIFO data segment.

12. How is the stack top address calculated?

The stack top address is calculated using the contents of the SS and SP register. The contents of stack segment (SS) register is shifted left by four bit positions (multiplied by (0h)) and the resulted 20-bit content is added with the 16-bit offset value of the stack pointer (SP) register.

13. What are macros?

Macros are small routines that are used to replace strings in the program. They can have parameters passed to them, which enhances the functionality of the micro itself‟

14.how are constants declared?

Constants are declared in the same way as variables, using the format: Const – Label EQU 012h

When the constants label is encountered, the constant numeric value is exchanged for the string.

15. Write an assembly language program for a 16-bit increment and will not affect the

contents of the accumulator.

MACRO inc16 variable; Increment two bytes starting at “variable” Local INC16 End

INC variable; Increment the low 8 bits

PUSH ACC

MOV A variable; Are the incremented low 8 bits = 0? JNZ INC 16 End

INC variable + 1

Inc16 End; Yes – increment the upper 8 bits

POP ACC

END MAC

16. What will happen if a label within a macro is not declared local?

If a label within a macro is not declared local, then at assembly time, there will be two types of errors:

I. The first will state that there are multiple labels in the source.

II. The second will indicate that jump instructions don’t know which one to use.

17. Write an assembly language program to load the accumulator with a constant value. MACRO invert value

if (value==0) MOV A, #1

else

clr A end if

END MAC.

18. What is the difference between the microprocessor and microcontroller?

Microprocessor does not contain RAM, ROM and I/O ports on the chip. But a microcontroller contains RAM, ROM and I/O ports and a timer all on a single chip.

19. What is assembler?

The assembler translates the assembly language program text which is given as input to the assembler to their binary equivalents known as object code. The time required to translate the assembly code to object code is called access time. The assembler checks for syntax errors & displays them before giving the object code.

20. What is loader?

The loader copies the program into the computer’s main memory at load time and begins the program execution at execution time.

21. What is linker?

A linker is a program used to join together several object files into one large object file. For large programs it is more efficient to divide the large program modules into smaller modules. Each module is individually written, tested & debugged. When all the modules work they are linked together to form a large functioning program.

22 .Explain ALIGN & ASSUME.

The ALIGN directive forces the assembler to align the next segment at an address divisible by specified divisor. The format is ALIGN number where number can be 2, 4, 8 or 16. Example ALIGN 8.

The ASSUME directive assigns a logical segment to a physical segment at any given time. It tells the assembler what address will be in the segment registers at execution time. Example ASSUME CS: code, DS: data, SS: stack

23. Explain PTR & GROUP

A program may contain several segments of the same type. The GROUP directive collects them under a single name so they can reside in a single segment, usually a data segment. The format is Name GROUP Seg-name,…..Seg-name

PTR is used to assign a specific type to a variable or a label. It is also used to override the declared type of a variable.

24. Explain about MODEL

This directive provides short cuts in defining segments. It initializes memory model before defining any segment. The memory model can be SMALL, MEDIUM,

COMPACT or LARGE.

25 Explain PROC & ENDP

PROC directive defines the procedures in the program. The procedure name must be unique. After PROC the term NEAR or FAR are used to specify the type of procedure. Example FACT PROC FAR. ENDP is used along with PROC and defines the end of the procedure.

26. Explain SEGMENT & ENDS

An assembly program in .EXE format consists of one or more segments. The starts of these segments are defined by SEGMENT and the end of the segment is indicated by ENDS directive. Format Name SEGMENT

27. Explain TITLE & TYPE

The TITLE directive helps to control the format of a listing of an assembled program. It causes a title for the program to print on line 2 of each page of the program listing. Maximum 60 characters are allowed. Format TITLE text. TYPE operator tells the assembler to determine the type of specified variable in bytes. For bytes the assembler gives a value 1, for word 2 & double word 4.

28 Define SOP

The segment override prefix allows the programmer to deviate from the default

segment

Eg     :         MOV CS: [BX] , AL

29 Define variable.

A variable is an identifier that is associated with the first byte of data item. In assembly language statement: COUNT DB 20H, COUNT is the variable.

30. What are procedures?

Procedures are a group of instructions stored as a separate program in memory and itis called from the main program whenever required. The type of procedure depends on where the procedures are stored in memory. If it is in the same code segment as that of the main program then it is a near procedure otherwise it is a far procedure.

31. Explain the linking process.

A linker is a program used to join together several object files into one large object file. The linker produces a link file which contains the binary codes for all the combined modules. It also produces a link map which contains the address information about the link files. The linker does not assign

Absolute addresses but only relative address starting from zero, so the programs are relocatable & can be put anywhere in memory to be run.

32, Define variable

A variable is an identifier that is associated with the first byte of data item. In assembly language statement: COUNT DB 20H, COUNT is the variable.

33. What are procedures?

Procedures are a group of instructions stored as a separate program in memory and it is called from the main program whenever required. The type of procedure depends on where the procedures are stored in memory. If it is in the same code segment as that of the main program then it is a near procedure otherwise it is a far procedure.

34. Explain the linking process.

A linker is a program used to join together several object files into one large object

file. The linker produces a link file which contains the binary codes for all the combined modules. It also produces a link map which contains the address information about the link files. The linker does not assign absolute addresses but only relative address starting from zero, so the programs are relocatable & can be put anywhere in memory to be run.

35. Compare Procedure & Macro.

Procedur

Accessed by CALL & RET instruction

during program execution

Machine code for instruction is put only once

With procedures less memory is required

Parameters can be passed in registers, memory locations or stack

Macro

Accessed during assembly with name to macro when defined

Machine code is generated for instruction each time when macro is called

With macro more memory is required

Parameters passed as part of statement which

36.            What is the maximum memory size that can be addressed by 8086?

In 8086, an memory location is addressed by 20 bit address and the address bus is 20 bit address and the address bus is 20 bits. So it can address up to one mega byte (2^20) of memory space.