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

Database management subsystem, (a) Explain, using suitable examples, the fu...

(a) Explain, using suitable examples, the functions of each of the sub system mentioned in the context of a large chain of supermarkets (i) Database Management Subsystem (ii)

Define the fundamentals of computer system, Define the Fundamentals of comp...

Define the Fundamentals of computer system A computer processes digital information. In order to do that it runs (executes) a machine language program. As an illustration, when

How dreamweaver work in layout view, Q. How Dreamweaver Work in Layout View...

Q. How Dreamweaver Work in Layout View? Dreamweaver has two visual design views-Standard view and Layout view. You will start by working in Layout view, which allows you to dra

What is a spool request, What is a Spool request? Spool requests are f...

What is a Spool request? Spool requests are formed during dialog or background processing and placed in the spool database with information about the printer and print format.

Illustrated three stages of data mining process, Illustrated three stages o...

Illustrated three stages of data mining process? Stage 1: Exploration: This stage generally starts along with data preparation that may involve cleaning data, selecting subse

What is the purpose of guard bits, What is the purpose of guard bits used i...

What is the purpose of guard bits used in floating point operations? The guard bits are the extra bits which are used to retain the in-between steps to enhance the accuracy in

Data rate limitations in PSTN's by using nyquist theorem, Explain with the ...

Explain with the help of Nyquist theorem, the data rate limitations in PSTN's. Data rates in PSTNs : A voice channel in a public switched telephone network is band restricted

Illustrate basic working of physical layer, Q. Illustrate basic working of ...

Q. Illustrate basic working of Physical layer? Physical layer: Physical layer is concerned with sending raw bits between source and destination nodes over a physical medium.

What is computer motherboard, If you open your computers case, the motherbo...

If you open your computers case, the motherboard is the flat, rectangular piece of circuit board to which the whole thing seems to connect to for one reason or one another. It'

Develop a regular expression for integer & real number, Develop a regular e...

Develop a regular expression for (i) Integer (ii) Real number (i) A regular expression for integer is [+ | -] (d)+ (ii) A regular expression for real number is [+

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