INT 21H (0x21) INT 21H (0x21) Function 03H (0x03) Auxiliary input 4H (0x04) Auxiliary output 05H (0x05) Printer output 06H (0x06) Direct console I/O 07H (0x07) Unfiltered character input without Echo

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INT 21H (0x21)

Function 03H (0x03) --> Auxiliary input

Call with: AH = 03H

Returns: AL = 8-bit input data

Comments:

It reads a character from the standard auxiliary device. The default is the first serial port (COM1).

If the auxiliary device sends data faster than your program can process it, characters may be lost. There is no way for a user program to read the status of the auxiliary device or to detect I/O errors such as lost characters, through this function call.

 

INT 21H (0x21)

Function 04H (0x04) --> Auxiliary output

Call with: AH = 04H
DL = 8-bit data for output

Returns: Nothing

Comments:

This function of INT 21H outputs a character to the standard auxiliary device. The default is the first serial port (COM1). Strings can also be sent to the auxiliary device by performing a write (INT 21H Function 40H) using the predefined handle for the standard auxiliary device (00034) or using a handle obtained by opening the logical device AUX.


INT 21H (0x21)

Function 05H (0x05) --> Printer output

Call with: AH = 05H
DL = 8-bit data for output

Returns: Nothing

Comments:

This function sends a character to the standard list device. The default device is the printer on the first parallel port (LPT1). Strings can also be sent to the printer by performing a write (INT 21H Function 40H) using the predefined handle for the standard printer device (0004H) or using a handle obtained by opening the logical device PRN or LPT1.

 

INT 21H (0x21)

Function 06H (0x06) --> Direct console I/O

Call with: AH = 06H
DL = function requested such that,
If output request, 00H-FEH
If input request, 0FFH

Returns: Nothing, If called with DL = 00H-0FEH

If called with DL = FFH and a character is ready
Zero flag = clear
AL = 8-bit input data

If called with DL = FFH and no character is ready
Zero flag = set

Comments:

It reads a character from the standard input device or writes a character to the standard output device. I/O may be redirected but if I/O has been redirected, there is no way to detect EOF or disk full. This function of INT 21H is used by programs that the need to read and write all possible characters and control codes without any interference from the operating system.

INT 21H (0x21)

Function 07H (0x07) --> Unfiltered character input without Echo

Call with: AH = 07H

Returns: AL = 8-bit input data

Comments:

This function reads a character from the standard input device without echoing it to the standard output device.

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Data Recovery with & without Programming


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