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

What technology used by magento, Magento uses PHP as a web server scripting...

Magento uses PHP as a web server scripting language and the MySQL Database. The data model is based on the Entity-attribute-value model that stores data objects in tree structures,

Rdbms, what is physical data structure in internals of rdbms?

what is physical data structure in internals of rdbms?

Convert the following from octal to binary, Q. Convert the following from o...

Q. Convert the following from octal to binary, decimal, hexadecimal and BCD. a) 7.7 b) 4037 c) 23.34

What is sap luw or update transaction, What is SAP LUW or Update Transactio...

What is SAP LUW or Update Transaction? Update transaction (or "SAP LUW") This is a set of updates terminated by an ABAP/4 commit.  A SAP LUW may last much longer than a data

Concept development journal, The Concept Development journal must contain: ...

The Concept Development journal must contain: An introductory paragraph detailing what conclusions you have drawn from your research and how you intend to proceed. This should b

What is a PCI bus and discuss its aspects and usage, What is a PCI bus? Dis...

What is a PCI bus? Discuss its aspects and usage. Peripheral Component Interconnect (PCI): This bus was developed by Intel and introduced in 1993. It is geared specifically to

Break keys, Like a normal read, your input should break on the new line cha...

Like a normal read, your input should break on the new line character "\n"   and also on the up and down arrow keys. You will process the input made by the user when he/she enters

Associativity of connectives - equivalences rules, Associativity of Connect...

Associativity of Connectives : Here brackets are very important in order to tell us where to perform calculations in arithmetic and logic. By using these brackets we evaluate

What is a priority interrupt, What is a Priority Interrupt? A priority ...

What is a Priority Interrupt? A priority interrupt is an interrupt that establishes a priority over the various sources to determine which condition is to be serviced first whe

Define the register addressing mode, Q. Define the Register Addressing mode...

Q. Define the Register Addressing mode? When operands are taken from registers implicitly or explicitly it is known as register addressing. These operands are termed as regis

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