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

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

How a typical dma controller can be interfaced to an 8086, Demonstrate how ...

Demonstrate how a typical DMA controller can be interfaced to an 8086/8085 based maximum mode system.  For 8088 in maximum mode: The RQ/GT0 and RQ/GT1 pins are used to is

Write a menu driven program, Q. Write a Menu driven program to convert the...

Q. Write a Menu driven program to convert the given Decimal number into Binary, Octal and Hexadecimal number. (Fractional numbers are allowed)

Harvard mark-I and the bug, The next important effort in the direction of d...

The next important effort in the direction of devising an electromechanical computer was made at Harvard University mutually sponsored by IBM and Department of UN Navy, Howard Aike

What is oo development, What is OO Development? OO development is a way...

What is OO Development? OO development is a way of thinking about software based on abstractions that exist in the actual world. Development refers to software lifecycle, desig

Explain cocomo model, A COCOMO model is :- COCOMO:- Constructive Cost Es...

A COCOMO model is :- COCOMO:- Constructive Cost Estimation Model.

Explain about butterfly permutation, Q. Explain about Butterfly permutation...

Q. Explain about Butterfly permutation? Butterfly permutation:  This kind of permutation is attained by interchanging the most significant bit in address with least significant

Interrupt - driven input-output, Q. Interrupt - Driven Input-output? Pr...

Q. Interrupt - Driven Input-output? Problem with programmed I/O is that processor has to wait a long time for I/O interface to see whether a device is free or waits until compl

Explain auto increment and auto decrement mode, Explain Auto increment and ...

Explain Auto increment and Auto decrement mode  The register is incremented or decremented after (or before) its value is used to access memory.  The address stored in the regi

Explain the working of hundred-line exchange, In a hundred-line exchange 24...

In a hundred-line exchange 24 two-motion selectors are used. Draw the schematic you suggest for this exchange and explain its working. How many simultaneous calls can be made durin

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