mov ah, 03h ;Auxiliary Input
int 21h
mov InputChar, al ;character from auxiliary input
Auxiliary Input (Function 03h) reads a character from the standard auxiliary device. If no character is available, MS-DOS waits.
This function has been superseded by Read File or Device (Function 3Fh).
This function has no parameters.
The AL register contains the ASCII value of the input character.
As this function receives characters from the standard auxiliary device, it does not save them in a buffer. Therefore, if the device is sending data faster than the program can process it, characters may be lost.
Function 04h Auxiliary Output
Function 3Fh Read File or Device