Assembler 3

5.41 21H Interruption
Purpose: To call on diverse DOS functions.

Syntax:

Int 21H

Note: When we work in TASM program is necessary to specify that the value we
are using is hexadecimal.

This interruption has several functions, to access each one of them it is necessary that the function number which is required at the moment of calling the interruption is in the AH register.

Functions to display information to the video.

02H Exhibits output
09H Chain Impression (video)
40H Writing in device/file

Functions to read information from the keyboard.

01H Input from the keyboard
0AH Input from the keyboard using buffer
3FH Reading from device/file

Functions to work with files.

In this section only the specific task of each function is exposed, for a
reference about the concepts used, refer to unit 7, titled : "Introduction
to file handling".

FCB Method

0FH Open file
14H Sequential reading
15H Sequential writing
16H Create file
21H Random reading
22H Random writing

Handles

3CH Create file
3DH Open file
3EH Close file driver
3FH Reading from file/device
40H Writing in file/device
42H Move pointer of reading/writing in file