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

Forward chaining - artificial intelligence, Forward Chaining - Artificial i...

Forward Chaining - Artificial intelligence: Imagine we have a set of axioms which we know are true statements regarding the world. If we set these to each be a starting state o

CRTscreen as a two-dimensional matrix, Explain the statement- CRT screen as...

Explain the statement- CRT screen as a two-dimensional matrix One can imagine the CRT screen as a two-dimensional matrix which has m rows and n  columns and this is usually ref

How the conversation speed of A/D converter is maximum, The conversation sp...

The conversation speed of an analog to digital converter is maximum with which technique? Ans. With parallel comparator AD converter technique the conversation speed of an ana

Inventor, I am the inventor of the railway signaling device now operated by...

I am the inventor of the railway signaling device now operated by timer. I wish to move on to the next phase where the equipment will be operated by DTMF codes. The device is a si

Determine the method for updating the main memory, The method for updating ...

The method for updating the main memory as soon as a word is removed from the Cache is known as  (A) Write-through                  (B) write-back   (C) protected write

Add references dialog box, What is the difference among "using System.Data;...

What is the difference among "using System.Data;" and directly adding the reference from "Add References Dialog Box"?  When you compile a program using command line, you add th

Variables and quantifiers for first-order models , Variables and Quantifier...

Variables and Quantifiers for First-order models -artificial intelligence: So what do sentences containing variables mean? In other words, how does first order model select whe

What are the limitations of traditional payment instruments, What are the l...

What are the limitations of traditional payment instruments? The limitations of traditional payment system are that they take a lot of time.  These systems needs manual work to

Data Warehousing Job Scheduling, 1) Define a job scheduling strategy that w...

1) Define a job scheduling strategy that will meet business requirement of reporting availability by 6am CST for the following cubes? Show the job scheduling dependencies in a pict

Example of calculate maximum access time & cost of switch, Calculate the ma...

Calculate the maximum access time that can be permitted for the data and control memories in a TSI switch with a single input and single output trunk multiplexing 2500 channels. Al

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