DATA SEGMENT
NUM1 DB ?
NUM2 DB ?
MSG1 DB 10,13,"ENTER FIRST NUMBER TO COMPARE : $"
MSG2 DB 10,13,"ENTER SECOND NUMBER TO COMPARE : $"
MSG3 DB 10,13,"SMALLER NUMBER IS : $"
ENDS
CODE SEGMENT
ASSUME DS:DATA CS:CODE
START:
MOV AX,DATA
MOV DS,AX
LEA DX,MSG1
MOV AH,9
INT 21H
MOV AH,1
INT 21H
MOV NUM1,AL
LEA DX,MSG2
MOV AH,9
INT 21H
MOV AH,1
INT 21H
MOV NUM2,AL
LEA DX,MSG3
MOV AH,9
INT 21H
MOV AL,NUM1
CMP AL,NUM2
JG SECOND
FIRST: MOV AH,2
MOV DL,NUM1
INT 21H
JMP EXIT
SECOND: MOV AH,2
MOV DL,NUM2
INT 21H
EXIT: 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.
LEA DX,MSG1
MOV AH,9
INT 21H
The above three line code is used to print String or Message present
in the character Array till $ symbol which tells the compiler to stop.
Now, lets understand line by line
LEA DX,MSG1 in this LEA stands for LOAD EFFECTIVE ADDRESS and it
loads the effective address of second element into the first element.
This same code can be interchangably written as MOV DX, OFFSET
MSG1 where OFFSET means effective address and MOV means move second
element into the first element.
MOV AH,9
INT 21H
The above two line code is used to PRINT the String or Message of the address present in DX register.
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 9 or 9h, That means PRINT the String or
Message of the address present in DX register.
MOV AH,1
INT 21H
MOV NUM1,AL
The above Four line code is used to Read a Character from Console and
save the value entered in variable NUM1 in its ASCII form. When you
enter 5 we see 35H,So by comparing 30H or 35H we get ASCII value
unchanged as we have to print the smaller back to console.
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 1 or 1h, That means READ a Character from
Console, Echo it on screen and save the value entered in AL register.
MOV NUM1,AL means move value in AL register into variable NUM1.
LEA DX,MSG2
MOV AH,9
INT 21H
The above two line code is used to PRINT the String or Message of the address present in DX register i.e. for MSG2.
MOV AH,1
INT 21H
MOV NUM2,AL
The above Four line code is used to Read a Character from Console and save the value entered in variable NUM2 in its ASCII form.
LEA DX,MSG3
MOV AH,9
INT 21H
The above two line code is used to PRINT the String or Message of the address present in DX register i.e. for MSG3.
MOV AL,NUM1
The above line code is to move NUM1 to AL register as we want to compare NUM1 with NUM2.
CMP AL,NUM2
JG SECOND
The above two line code is used to compare two variables and jump to the respective LABEL.
As we know the programs work only with the instructions in the instruction set. Instruction ADD is used to add to numbers in the following permutations above. REG stands for Registers (Eg. AX, BX, CX, DX ). memory stands for Variable or Address. immediate stands for Numbers or Values. Let us understand the meanings of the above permutations.
First permutation :- REG , memory means Register can be added with memory.
Second permutation :- memory , REG means memory can be added with Register.
Third permutation :- REG, REG means Register can be added with Register.
Fourth permutation :- memory , immediate means memory can be added with immediate.
Fifth permutation :- REG, immediate means Register can be added with immediate.
Note :- In the permutations above it will work only in the order
mentioned above and not by interchanging the first to second and second
to first.
Now, we have understood part of it to add to number we can write CMP NUM1, NUM2, But there is no permutation for CMP memory, memory,
Hence we have to send one number to AL or AX depending on DB or DW. The
result of Comparision is not stored anywhere, but flags are set
according to result.
JG SECOND is Short Jump if first
operand is Greater then second operand (as set by CMP instruction).
Signed. SECOND is the label where the compiler will JUMP.
FIRST: MOV AH,2
MOV DL,NUM1
INT 21H
JMP EXIT
The above Four line code is used to Write a Character on Console present in DL register i.e. NUM1.
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 2 or 2h, That means WRITE a Character on
Console present in DL register hence the value to be printed is moved to
DL register. Here we are printing NUM1 variable. JMP is Unconditional
Jump. Label FIRST is to tell that first number is going to be printed
and If there is no JUMP in between then Label SECOND will be printed
showing both Variables on console. Hence JMP EXIT so that Label SECOND
is not executed.
SECOND: MOV AH,2
MOV DL,NUM2
INT 21H
The above Three line code is used to Write a Character on Console present in DL register i.e. NUM2.
EXIT: 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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