DATA SEGMENT
NUM1 DB 5
NUM2 DB 9
NUM3 DB 7
AVG DB ?
ENDS
CODE SEGMENT
ASSUME DS:DATA CS:CODE
START:
MOV AX,DATA
MOV DS,AX
MOV AL,NUM1
ADD AL,NUM2
ADD AL,NUM3
MOV AH,0
MOV DL,3
DIV DL
MOV AVG,AL
MOV AH,4CH
INT 21H
ENDS
END START
Explanation :
In this Assembly Language Programming, A single program is divided
into four Segments which are 1. Data Segment, 2. Code Segment, 3. Stack
Segment, and 4. Extra Segment. Now, from these one is compulsory i.e.
Code Segment if at all you don’t need variable(s) for your program.if
you need variable(s) for your program you will need two Segments i.e.
Code Segment and Data Segment.
CODE SEGMENT
CODE SEGMENT is the starting point of the Code Segment in a Program
and CODE is the name given to this segment and SEGMENT is the keyword
for defining Segments, Where we can write the coding of the program.
ASSUME DS:DATA CS:CODE
In this Assembly Language Programming, their are Different Registers
present for Different Purpose So we have to assume DATA is the name
given to Data Segment register and CODE is the name given to Code
Segment register (SS,ES are used in the same way as CS,DS )
START:
START is the label used to show the starting point of the code which
is written in the Code Segment. : is used to define a label as in C
programming.
MOV AX,DATA
MOV DS,AX
After Assuming DATA and CODE Segment, Still it is compulsory to
initialize Data Segment to DS register. MOV is a keyword to move the
second element into the first element. But we cannot move DATA Directly
to DS due to MOV commands restriction, Hence we move DATA to AX and then
from AX to DS. AX is the first and most important register in the ALU
unit. This part is also called INITIALIZATION OF DATA SEGMENT and It is
important so that the Data elements or variables in the DATA Segment are
made accessable. Other Segments are not needed to be initialized, Only
assuming is enhalf.
MOV AL,NUM1
ADD AL,NUM2
ADD AL,NUM3
The above three line code is used to add the three variables and the result in saved by default in AL reister.
Now we have to send one number to AL or AX depending on DB or DW. AX
Register is called Accumalator. and is used for holding the result of
Addition in it After Addition. Now we are taking DB, So we have t0
instruction MOV AL,NUM1 move NUM1 variable value to AL Register. After moving NUM1 to AL, We can Add REG to memory, So we have ADD AL,NUM2 or (We can Add memory to REG , So we have ADD NUM2,AL)
Both are allowed as per permutations so use one from two. Now, the
Resultant Value is saved in Accumalator AL for DB and AX for DW.
MOV AH,0
MOV DL,3
DIV DL
So divide Resultant value by 3 so that Average is found in AL
register, But the DIV instruction is used to divide AX and Not only AL
register. Hence the unwanted value (garbage value) in AH register is
removed by assigning ZERO to it. i.e. MOV AH,0
DIV instruction only works with REG or MEMORY hence we cannot use DIV
3 where 3 is immediate, So we have to move 3 to DL register (we can
take any register) i.e. MOV DL,3 and Then DIV DL
Now DIV DL will Divide AX register with 3 which is passed to DL
register and Result of division is present in AL register so move the
resultant value i.e. Average to variable by instruction MOV AVG,AL
MOV AH,4CH
INT 21H
The above two line code is used to exit to dos or exit to operating
system. Standard Input and Standard Output related Interupts are found
in INT 21H which is also called as DOS interrupt. It works with the
value of AH register, If the Value is 4ch, That means Return to
Operating System or DOS which is the End of the program.
CODE ENDS
CODE ENDS is the End point of the Code Segment in a Program. We can
write just ENDS But to differentiate the end of which segment it is of
which we have to write the same name given to the Code Segment.
END START
END START is the end of the label used to show the ending point of the code which is written in the Code Segment.
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