DATA SEGMENT
T DB ?
RES DB 10 DUP ('$')
MSG1 DB "ENTER TEMPERATURE IN CELSIUS (ONLY IN 2 DIGITS) : $"
MSG2 DB 10,13,"CONVERTED IS FAHRENHEIT (TEMPERATURE) : $"
DATA 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
SUB AL,30H
MOV AH,0
MOV BL,10
MUL BL
MOV BL,AL
MOV AH,1
INT 21H
SUB AL,30H
MOV AH,0
ADD AL,BL
MOV T,AL
MOV DL,9
MUL DL
MOV BL,5
DIV BL
MOV AH,0
ADD AL,32
LEA SI,RES
CALL HEX2DEC
LEA DX,MSG2
MOV AH,9
INT 21H
LEA DX,RES
MOV AH,9
INT 21H
MOV AH,4CH
INT 21H
CODE ENDS
HEX2DEC PROC NEAR
MOV CX,0
MOV BX,10
LOOP1: MOV DX,0
DIV BX
ADD DL,30H
PUSH DX
INC CX
CMP AX,9
JG LOOP1
ADD AL,30H
MOV [SI],AL
LOOP2: POP AX
INC SI
MOV [SI],AL
LOOP LOOP2
RET
HEX2DEC ENDP
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.
Now, We have to Scan two values from the Screen BY reading two individual
Character and convert it back to the original value entered. What we will do is
except 25 in this 32H and 35H will be two ASCII values received. From 32H
first digit substract 30H i.e. 32 -30 = 2, Muliply two with 10 to
get 20 i.e. 2*10 = 20, 35h will From 35H Second digit substract
30H i.e. 35 -30 = 5, Add five with 20 to get i.e. 20 +
5 = 25.
MOV AH,1
INT 21H
The above two line code is used to Read a Character from Console (First
Digit).
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.
SUB AL,30H
MOV AH,0
Convert AL to its BCD form. This can be done by subtracting 30H i.e.
SUB AL,30H. The value coming from Console is Basically in ASCII form. eg. When
you enter 5 we see 35H,So by subtracting 30H we get back to value as 5. SUB
AL,30H means subtracting 30H from AL. MOV
AH,0 is used to clear the unwanted value (garbage value)
in AH register is removed by assigning ZERO to it.
Now, Let me tell you why we need to clear AH register. Because we will
Multiply AL register by 10. and If we do not clear unwanted value we will get
Wrong Product.
MOV BL,10
MUL BL
MOV BL,AL
The above three line code is used to Move 10 to BL
register and Multiply 10 with AL register
MUL 10 cannot be used hence We first move 10 to BL register i.e. MOV
BL,10. After that MUL BL
in this line BX register will be Multiplied with AX register (BY
DEFAULT) in which the resultant value of 10X is present. MOV
BL,AL is used to move Result to BL.
MOV AH,1
INT 21H
The above two line code is used to Read a Character from Console(Second
Digit).
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.
SUB AL,30H
MOV AH,0
ADD AL,BL
MOV T,AL
Convert AL to its BCD form. This can be done by subtracting 30H i.e.
SUB AL,30H. The value coming from Console is Basically in ASCII form. eg. When
you enter 5 we see 35H,So by subtracting 30H we get back to value as 5. SUB
AL,30H means subtracting 30H from AL. MOV
AH,0 is used to clear the unwanted value (garbage value)
in AH register is removed by assigning ZERO to it. ADD AL,BL
adding AL with BL register to get the Original Value entered by User. MOV
T,AL means move value in AL register into variable T.
Now, Let me tell you why we need to clear AH register. Because we will
Multiply AL register by 10. and If we do not clear unwanted value we will get
Wrong Product.
MOV DL,9
MUL DL
The above line code is used to Multiply AX register by 9
i.e. Celsius value present in AX register
MUL 9 cannot be used hence We first move 9 to DL register i.e. MOV
DL,9. After that MUL DL
in this line DL register will be Multiplied with AX register (BY
DEFAULT) in which the Temperature in Celsius value is present. Now, This will
give (Celsius * 9).
MOV BL,5
DIV BL
The above line code is used to Divide AX register by 5
i.e. (Celsius * 9) value present in AX register
DIV 5 cannot be used hence We first move 5 to BL register
i.e. MOV BL,5. After that DIV
BL in this line value in BL
register will Divide AX register (BY DEFAULT) in which the
resultant value of (Celsius * 9) is present. Now, This will give (Celsius
* 9 / 5).
MOV AH,0
ADD AL,32
The above line code is used to ADD 32 to BX register and
Store the resultant { (Celsius * 9 / 5) + 32 } in
it. MOV AH,0 is used to clear the unwanted value
(garbage value) in AH register is removed by assigning ZERO to it. ADD
AL,32 is used to ADD AL
register to 32 and Store the resultant { (Celsius
* 9 / 5) + 32 } in it.
LEA SI,RES
CALL HEX2DEC
The above Two line code is used to initialize RES to SI register
and Call Procedure HEX2DEC which will covert AX register value as result
and Print it on user screen.
LEA SI,RES is used to Load Effective
Address of RES variable to SI Register. CALL HEX2DEC is
used to Call a Procedure named HEX2DEC
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.
LEA DX,RES
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. As we have initialized all the values in an Array to $ you
will think what will be printed. The procedure is going to change the Array to
its Resultant Decimal equivalent printable form i.e. ASCII form of a digit
number.
Now, lets understand line by line
LEA DX,RES 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 RES 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,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.
PROCEDURE Code starts here:
Procedure is a part of code that can be called from a program in order to
perform specific task.
HEX2DEC PROC NEAR
This line of code is used to start a procedure code and we can make out the
procedure by the keyword PROC which tells us the procedure is
started. In assembly language we have two types of Procedures one is NEAR
and other is FAR. NEAR is used to call the Procedure within the
program whereas FAR is used to call the procedure outside
the program. HEX2DEC is only the Name given to the
Procedure Code.
MOV CX,0
MOV BX,10
MOV CX,0 is used to move or assign value 0
(decimal value) to CX. The program which we are wishing to write is
to covert HexaDecimal value to Decimal value, In which we
will divide the number till the Quotient is going to be
Zero. CX register ( CX is also Called COUNTER). CX register will
count the number digit generated by dividing the Hexadecimal number by Base
value of Decimal i.e.Ten. MOV BX,10 in this
Base value 10 is moved to BX register, So that it is used to divide hexa number
by 10.
LOOP1: MOV DX,0
LOOP1: is a LABEL and all the words ending in colon (:) are Labels. MOV
DX,0 is used to clear the unwanted value (garbage value) in DX
register is removed by assigning ZERO to it. First Loop starts here.
DIV BX
ADD DL,30H
DIV instruction only works with REG or MEMORY hence we cannot use
DIV 10 where 10 is immediate, So we have to move 10 to BX
register (we can take any register) this we have already done
above and Then DIV BX Now
DIV BX will Divide AX register with 10 which is passed to BX
register and Result of division is present in AX register contains
Quotientand DX register contains Remainder. Here we will not touch Quotient AX
as it will be used for furture Division, But DX Remainder will be Decimal
Digit and will always be less than Ten so the value will be in DL register only
and to make it printable on Console (Screen) we have to add 30H
So that it will become a ASCII character and will be saved in Charater Array
and will be printed as String later So ADD DL,30H.
PUSH DX
INC CX
PUSH is a stack function. Stack is an area of memory for keeping
temporary data. PUSH and POP are two stack operations which stores or gets 16
bits of data. PUSH DX stores 16 bit data
inside DX register into Stack Area. INC is a instruction for Increment the
present in Register or Memory. INC CX will increment
the value present in CX register by One. Here we are using CX register as a
counter and counting the numbers of digits in their ASCII form which are
pushed into Stack. So that the same count will help to POP the values out of
Stack.
MOV CX,10
MOV CX,10 is used to move or
assign value 10 (decimal value) to CX. The program which we are
wishing to write is to input ten characters from console which will be entered
by the user, Hence to do so we need a loop construct. In assembly
programming language we have a LOOP instruction. This works with
two other helpers which are Label and Counter. The Loop start with LABEL
and ends with LOOP instruction with the same LABEL name with it. the execution
of the Loop depends on the value in CX register ( CX is also Called
COUNTER).
CMP AX,9
JG LOOP1
CMP AX,9 is used to compare AX
register with 9 and jump if AX is greater to the respective LABEL
LOOP1. The result of Comparision is not stored anywhere, but flags
are set according to result. 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 Loop ends
here. Note :- this loop is without LOOP keyword and depends upon the number to
be converted.
ADD AL,30H
MOV [SI],AL
ADD AL,30H The Last Remainder will
be Decimal Digit in AX register only as the number cannot be divided
future and will always be less than Ten so the value will be in AL register
only and to make it printable on Console (Screen) we have to add
30H So that it will become a ASCII character and will be saved in
Charater Array and will be printed as String later. MOV [SI],AL
Saving the Characters in Character Array (i.e. String) is done by Moving
AL register to Address of SI register which is represented in Square Brackets
i.e. [SI]. SI is assigned with the Character Array i.e. RES.
LOOP2: POP AX
INC SI
LOOP2: is a LABEL and all the words ending
in colon (:) are Labels. POP is a stack function. Stack is an area of
memory for keeping temporary data. PUSH and POP are two stack operations which
stores or gets 16 bits of data. POP AX gets 16
bit data to AX register from Top of Stack. INC CX will
increment the value present in CX register by One. Here we are using CX
register as a counter and counting the numbers of digits in their ASCII
form which are pushed into Stack. So that the same count will help to POP the
values out of Stack and save it in AX register. Second Loop starts here.
MOV [SI],AL
The values out of Stack saved in AX register saved in string in
this Loop. MOV [SI],AL Saving the
Characters in Character Array (i.e. String) is done by Moving AL register to
Address of SI register which is represented in Square Brackets i.e. [SI]. SI is
assigned with the Character Array i.e. RES.
LOOP LOOP2
This end of loop. In assembly programming language we have a
LOOP instruction. This works with two other helpers which are
Label and Counter. The Loop start with LABEL and ends with LOOP instruction
with the same LABEL name with it. the execution of the Loop depends on the
value in CX register ( CX is also Called COUNTER).
RET
RET is a return instruction. This instruction
is used only if the control is been passed to the code outside Main like
to Procedure. this return the control to the place where the Procudure was
called.
HEX2DEC ENDP
HEX2DEC ENDP is the End point of
the Procedure in a Program.
This line of code is used to end the procedure code and we can
make out the procedure by the keyword ENDP which tells us the procedure is
ended. In assembly language we have two types of Procedures one is NEAR
and other is FAR. NEAR is used to call the Procedure within the
program whereas FAR is used to call the procedure outside the program. HEX2DEC
is only the Name given to the Procedure Code.
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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