Invoked for each keystroke by the ROM BIOS's Int 09H keyboard interrupt handler.
Call with:
AH = 4FH
AL = scan code
Returns:
If scan code consumed
Carry flag = clear
If scan code not consumed
Carry flag = set
AL = unchanged or new scan code
Notes:
An operating system or a resident utility can capture this function to filter the raw keyboard data stream. The new handler can substitute a new scan code, return the same scan code, or return the carry flag clear causing the keystroke to be discarded. The default ROM BIOS routine simply returns the scan code unchanged.
A program can call Int 15H Function C0H to determine whether the host machine's ROM BIOS supports this keyboard intercept.