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

Spatial domain interpolation, Transfer Domain Create an interpolation al...

Transfer Domain Create an interpolation algorithm using the fast Fourier transformer. Assess the performance of the algorithm by using the PSNR and SSIM.  Compare your results w

Explain public key encryption, Public Key Encryption A cryptographic sy...

Public Key Encryption A cryptographic system that uses two-keys-a public  key known to everyone and a private or secret key known only to the recipient of the message. An si

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

What is pipelining, What is pipelining? The overlapping of implementati...

What is pipelining? The overlapping of implementation of successive instructions is known as pipelining.

Enumerate about the decimal arithmetic unit, Enumerate about the Decimal Ar...

Enumerate about the Decimal Arithmetic Unit The user of the computer input data in decimal numbers and receives output in the decimal form. But a CPU with ALU can perform arith

Multi-threaded processors, Multi-Threaded Processors In unit 2, we have...

Multi-Threaded Processors In unit 2, we have gone through the use of distributed shared memory in parallel computer architecture. Although the use of distributed shared memory

Synchronous, What are differences between Synchronous, Asynchronous and I s...

What are differences between Synchronous, Asynchronous and I synchronous communication? Sending data encoded in your signal needs that the sender and receiver are both by using

Explain the working of dynamic ram - computer memory, Explain the working o...

Explain the working of Dynamic RAM? A plain piece of hardware called a DRAM controller can be used to make DRAM behave more like SRAM and the job of the DRAM controller is to p

What are the different sections of a report, What are the different section...

What are the different sections of a report? A report is categorized into many sections: The Report header: In this you place a control which must appear only at the startin

Explain the reference count - free memory areas, Explain the Reference Coun...

Explain the Reference Count The system relates a reference count along with each memory area to point out the number of its active users. This number is incremented while a us

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