three digits are interpreted as a character code
and
are
transmitted through
the
keyboard routine
to
the system or
application program. Alt is handled within the keyboard routine.
Caps Lock
This key shifts keys
16-25,30-38,
and
44-50
to
uppercase.
Pressing the
Caps
Lock
key a second time reverses the action.
Caps
Lock
is handled within
the
keyboard routine.
ScroD Lock
This key is interpreted
by
appropriate application programs as
indicating
that
use
of
the cursor-control keys should cause
windowing over the text rather
than
cursor movement. Pressing
the Scroll Lock key a second time reverses the action. The
keyboard routine simply records the current shift state
of
the
Scroll Lock key.
It
is the responsibility of the system
or
application program
to
perform the function.
Shift Key Priorities and Combinations
If
combinations
of
the Alt, Ctrl,
and
Shift keys are pressed
and
only one is valid, the precedence is as follows: the Alt key is first,
the Ctrl key is second,
and
the Shift key is third. The only valid
combination is Alt
and
Ctrl, which is used in the system reset
function.
Special Handling
System Reset
The combination
of
the Alt, Ctrl, and Del keys will result in the
keyboard routine initiating the equivalent of a system reset.
System reset is handled within the keyboard routine.
5-20
System BIOS
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