DOS FUNCTIONS AND INTERRUPTS

DOS FUNCTIONS AND INTERRUPTS (KEYBOARD AND VIDEO PROCESSING)
The Intel CPU recognizes two types of interrupts namely hardware interrupt when a peripheral devices needs attention from the CPU and software interrupt that is call to a subroutine located in the operating system. The common software interrupts used here are INT 10H for video services and INT 21H for DOS services.
INT 21H:
It is called the DOS function call for keyboard operations follow the function number. The service functions are listed below:
# 00H- It terminates the current program.
- Generally not used, function 4CH is used instead.
# 01H- Read a character with echo
- Wait for a character if buffer is empty
- Character read is returned in AL in ASCII value
# 02H- Display single character
- Sends the characters in DL to display
- MOV AH, 02H
- MOV DL, ‘A’ ; move Dl, 65
- INT 21H
# 03H and 04H – Auxiliary input/output
- INT 14H is preferred.
# 05H – Printer service
- Sends the character in DL to printer
# 06H- Direct keyboard and display
- Displays the character in DL.
# 07H- waits for a character from standard input

DOS FUNCTIONS AND INTERRUPTS (KEYBOARD AND VIDEO PROCESSING)
The Intel CPU recognizes two types of interrupts namely hardware interrupt when a peripheral devices needs attention from the CPU and software interrupt that is call to a subroutine located in the operating system. The common software interrupts used here are INT 10H for video services and INT 21H for DOS services.
INT 21H:
It is called the DOS function call for keyboard operations follow the function number. The service functions are listed below:
# 00H- It terminates the current program.
- Generally not used, function 4CH is used instead.
# 01H- Read a character with echo
- Wait for a character if buffer is empty
- Character read is returned in AL in ASCII value
# 02H- Display single character
- Sends the characters in DL to display
- MOV AH, 02H
- MOV DL, ‘A’ ; move Dl, 65
- INT 21H
# 03H and 04H – Auxiliary input/output
- INT 14H is preferred.
# 05H – Printer service
- Sends the character in DL to printer
# 06H- Direct keyboard and display
- Displays the character in DL.
# 07H- waits for a character from standard input