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SECTION 6 Conversions and Interfaces
PEN*KEY
R
6100 Computer Programmer’s Reference Guide 6-35
Standard Keyboard Interface: INT 09h
Matrix scan codes are converted to PCĆcompatible scan codes before Interrupt
09h is issued. Standard scan codes are read from port 60h. If the scan code is
not a request for an internal function or a control key press, both the character
code and scan code (two bytes) are placed in a 16Ćword circular buffer at the posiĆ
tion pointed to by the keyboard tail buffer pointer. The tail pointer is then inĆ
cremented by two and allowed to wrap around the buffer.
INT 09h supports the following internal functions:
Function Description
CtrlĆAltĆDel System Reset. Detection of a ControlĆAltĆDelete sequence causes the handler to set
the reset flag to 1234h (do not do a memory test) and jump to the POST.
CtrlĆScroll Lock Break. The CtlĆBreak sequence issues an INT 1Bh and returns the value zero.
ShiftĆPrtSc Print Screen. ShiftĆPrint Screen issues an INT 05h.
CtrlĆNum Lock Pause. The Pause key causes the handler to issue INT 15, Function 41h to wait for a
valid ASCII keystroke.
The keyboard handler issues an INT 15h, Function 91h with AL = 2 on return
from interrupt to indicate a keystroke is available for keys that return values.
The keyboard handler issues an INT 15h, Function 4Fh after reading the scan
code from port 60, for the system to replace or absorb the scan code. On return
from INT 15, the code is processed if the carry flag is set. Otherwise, the key is
not processed.
The SYSREQ key issues an INT 15, Function 85h to inform the system of a
make or break operation of the SYSREQ key.
Control, Alt , Shift keys, Num Lock, Scroll Lock, Pause, and Caps Lock key
presses update the keyboard mode and type flags. No character code is returned
by the keyboard BIOS for these key presses. Applications that want to know the
status of these flags may inquire the keyboard BIOS through Interrupt 16h,
Function 02h.
The Scan Code tables that list the character codes for ATĆcompatible keyboards,
refer to the Keyboard Services Interrupt definitions (INT 16h), page 6Ć87.
6. Conversions and
Interfaces