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

Explain the term- scan insertion, Explain the term- Scan Insertion Sca...

Explain the term- Scan Insertion Scan Insertion is completed by a tool and results in all (or most) of your design's flip-flops to be changed by special "Scan Flip-flops". Sca

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

Explain parallelism conditions, Parallelism Conditions As discussed ear...

Parallelism Conditions As discussed earlier, parallel computing needs the segments to be executed in parallel should be independent of each other. So before executing paralleli

Difference between leave transaction and call transaction, What is the diff...

What is the difference between Leave Transaction and Call Transaction? In contrast to LEAVE TO TRANSACTION, the CALL TRANSACTION  statement causes the system to start a new SAP

Find minimal expression for sop. draw gate network, Q Consider the followin...

Q Consider the following expression. Assume that complement inputs are available. F(A,B,C,D) = ∑m (1,2,6,9,10,14) + ∑d (4,7,8,11,12) a. Find minimal expression for SOP. Draw

Payment, how can get payment

how can get payment

Which device converts BCD to seven segment, A device which converts BCD to ...

A device which converts BCD to Seven Segment is called ? Ans. DECODER is a device that converts BCD to Seven Segment. This coverts binary words in alphanumeric characters.

What do you mean by inline function, The idea behind inline functions is to...

The idea behind inline functions is to insert the code of a known function at the point where the function is called. If done carefully, this can improve the application's performa

Define a segment index or an internal index, The field that contains a segm...

The field that contains a segment index or an internal index is called ? Ans. Target datum consists of a segment index or an internal index.

What are null values, What are null values? If the value of a field in ...

What are null values? If the value of a field in a table is indeterminate or unknown, it is known as a null value.

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