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

Prove the equations using the boolean algebraic theorems, Prove the equatio...

Prove the equations A + A‾ .B + A.B‾ = A + B using the Boolean algebraic theorems ? Ans. The equation is A + A‾.B + A.B‾ = A + B L.H.S. = A + A‾ .B + A.B‾ = (A + A.B‾) + A‾.B

Discuss the process of data mining, Discuss the process of data mining? ...

Discuss the process of data mining? The process of data mining having of three stages: (1)The initial exploration (2) Model building or pattern identification with validat

Computers, Purpose: Front line client service. Make bookings for vehicle se...

Purpose: Front line client service. Make bookings for vehicle servicing, accesses client database, prints invoices for clients etc. The mechanics complete worksheets for the variou

What is a convertor?, Converter is an application that converts distance me...

Converter is an application that converts distance measurements among metric and U.S units.

Explain open-systems interconnections architecture model, Q. Explain Open-s...

Q. Explain Open-systems interconnections architecture model The most common network architecture model is the open-systems interconnections (OSI). Figure shows the ISO (Intern

What are the principles of transport layer, Q. What are the principles of t...

Q. What are the principles of transport layer? Transport layer: This layer is the first end-to-end layer. Header of transport layer includes information which helps send the

Disk operating system, Q. Disk operating system? The operating system (...

Q. Disk operating system? The operating system (OS) is the first program that should be loaded into the memory of your PC before you can use it for any application. You can st

Show a string in assembly language, Q. Show a string in assembly language? ...

Q. Show a string in assembly language? MOV AH, 09H MOV DX, OFFSET   BUFF INT    21H Here data in input buffer stored in data segment is intended to be displayed on mo

Write an algorithm to outline the macro-expansion, Write an algorithm to ou...

Write an algorithm to outline the macro-expansion using macro-expansion counter. The flow of control throughout macro expansion can be implemented by using a MEC that is macro-

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