Break
The combination
of
the Ctrl and Break keys will result in the
keyboard routine signaling interrupt hex
lA.
Also the extended
characters
(AL
= hex 00,
AH
= hex 00) will be returned.
Pause
The combination
of
the Ctrl and Num Lock keys will cause the
keyboard interrupt routine to loop, waiting for any key except the
Num Lock key to be pressed. This provides a system- or
application-transparent method
of
temporarily suspending list,
print, and so on, and then resuming the operation. The
"unpause"
key
is
thrown away. Pause
is
handled within the
keyboard routine.
Print
Screen
The combination of the Shift and PrtSc (key 55) keys will result
in
an
interrupt invoking the print screen routine. This routine
works in the alphanumeric
or
graphics mode, with unrecognizable
characters printing as blanks.
Extended Functions
The keyboard routine does its own buffering. The keyboard
buffer
is
large enough that few typists will ever fill it. However, if
a key
is
pressed when the buffer
is
full, the key will be ignored
and the "bell" will sound.
Also, the keyboard routine suppresses the typematic action of the
following keys: Ctrl, Shift, Alt, Num Lock, Scroll Lock, Caps
Lock,
and
Ins.
System BIOS
5-21
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