Dos function calls, Computer Engineering

Assignment Help:

INT 21H supports about 100 different functions. A function is recognised by putting the function number in AH register. For illustration if we want to call function number 01 then we place this value in AH register first by employing MOV instruction and after that call INT 21H:

Some significant DOS function calls are: 

DOS

Function Call 

Purpose

Example

AH = 01H

 

For reading a single character from keyboardand echo it on monitor. The input value is put inAL register.

To get one character input in a variable in data segment you may include the following in the code segment:

MOV AH,01

INT 21H

MOV X, AL 

(Please note that interrupt call will return value in AL which is being transferred to variable of data segment X. X must be byte type).

AH = 02H

This function prints 8 bit data (normally ASCII) that is stored in DL register on the screen.

To print a character let say '?' on the screen we may have to use following set of commands:

MOV AH, 02H;

MOV DL, '?'

INT 21H

AH = 08H

This is an input function for inputting one character. This is same as AH = 01H functions with the only difference that value does not get displayed on the screen.

Same example as 01 can be used only difference in this case would be that theinput character wouldn't get displayed

MOV AH, 08H

INT 21H

MOV X, AL

AH = 09H

This program outputs a string whose offset is stored in DX register and that is terminated using a $ character. One can print newline, tab character also. 

To print a string "hello world" followed by a carriage return (control character) we may have to use the following assembly program segment.

 

Example of

AH = 09H

CR EQU ODH 

; ASCII code of carriage return.

DATA SEGMENT 

STRING DB 'HELLO WORLD', CR, '$'

DATA ENDS

CODE SEGMENT

         :

      MOV AX, DATA

      MOV DS, AX

      MOV AH, 09H

      MOV DX, OFFSET STRING

; Store the offset of string in DX register.

      INT 21H

AH = 0AH

For input of string up to 255 characters. The stringis stored in a buffer.

Look in the examples given.

AH = 4CH

Return to DOS

 


Related Discussions:- Dos function calls

What is pure semiconductors, Q. What is Pure semiconductors? Pure semic...

Q. What is Pure semiconductors? Pure semiconductors, known as intrinsic semiconductors, have very few charge carriers and may hence be classified as almost insulators or very p

Paging supervisor - computer architecture, Paging supervisor: This par...

Paging supervisor: This part of the operating system built and manages the page tables. If the  due to dynamic address translation hardware a page fault occurs exception then

Define elimination of common sub expression, Explain Elimination of common ...

Explain Elimination of common sub expression during code optimization An optimizing transformation is a regulation for rewriting a segment of a program to enhance its execution

Serial execution and parallel execution, Serial Execution Execution of ...

Serial Execution Execution of a program consecutively, one statement at a time. In the easiest sense, this is what occurs on a one processor machine. However, even many of the

Which function type is used for using "at exit-command", Which Function typ...

Which Function type has to be used for using "at exit-command" ? To Use AT EXIT - COMMAND, We must assign a function Type "E" to the relevant function in the MENU Painter OR S

Find 9''s complement for decimal number, Q. Find 9's complement for decimal...

Q. Find 9's complement for decimal number? The 9's complement is achieved by subtracting every digit of number from 9 (the highest digit value). Let's assume that we want to si

Define parameters used in program annotation, Q. Define Parameters used in ...

Q. Define Parameters used in Program Annotation? Parameters: A parameter refines and extends the meaning that assembler attributes to keyword in a statement.  Number of param

C program, find area uder the curve y=f(x) between x=a and x=b Posted Date...

find area uder the curve y=f(x) between x=a and x=b Posted Date: 9/1/2012 1:50:09 AM

What is performance testing in loadrunner, Timing for both read and update ...

Timing for both read and update transactions should be gathered to verify whether system functions are being performed in an acceptable timeframe. This should be done standalone an

Explain the disadvantages of random scan display, Disadvantages of random s...

Disadvantages of random scan display - Just by wire-frame, it is almost impossible to create images with shaded objects or areas filled with a given colour. - In case

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd