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

Asymptotic notations, Asymptotic Notations These notations are used fo...

Asymptotic Notations These notations are used for evaluating functions. Assume we have two functions f(n) and g(n) defined on real numbers, Theta Notation Big Notation

Spmd model for programming, Q. SPMD model for programming? A normal ass...

Q. SPMD model for programming? A normal assumption was that it must be possible and not too hard to capture the SPMD model for programming MIMD computers in data parallel langu

Describe about remote-load latency problem, Q. Describe about Remote-load L...

Q. Describe about Remote-load Latency Problem? When one processor requires some remote loading of data from other nodes then processor has to wait for these two remote load ope

What is arithmetic and logic unit, What is Arithmetic and Logic Unit Ar...

What is Arithmetic and Logic Unit Arithmetic and Logic Unit: The ALU is the 'core' of any processor. It implements all arithmetic operations (addition, multiplication, subtract

Give example of real time processing, Give example of Real time (transactio...

Give example of Real time (transaction) processing Using this illustration of booking seats on a flight, below sequence of events would occur: -  Customer/travel agent conta

How do you track down a transition by name, Question 1: a) How do you ...

Question 1: a) How do you track down a transition by name? b) Why Premiere Pro is considered a non-linear editor? c) Explain clearly the main problem that may arise wh

Algorithm, i need algorithm for padovan string

i need algorithm for padovan string

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

Mapping, what is transform mapping and transaction mapping?

what is transform mapping and transaction mapping?

Sigmoid units, Sigmoid units: Always remember that the function inside...

Sigmoid units: Always remember that the function inside units take as input the weighted sum, S and of the values coming from the units connected to it. However the function i

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