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Extended Codes
Extended Functions
For certain functions that cannot be represented in the standard
ASCII code, an extended code is used. A character code of 000
(Null) is returned in AL. This indicates that the system or
application program should examine a second code that will
indicate the actual function. Usually, but not always, this second
code is the scan code of the primary key that was pressed. This
code is returned in AH.
Shift States
Most shift states are handled within the keyboard routine and are
not apparent to the system or application program. In any case,
the current set of active shift states is available by calling an entry
point in the ROM keyboard routine. The key numbers are shown
on the keyboard diagrams beginning on page 4-12. The following
keys result in altered shift states:
Shift
This key temporarily shifts keys 2-13,15-27,30-41,43-53,55,
59-68 to uppercase (base case if in Caps Lock state). Also, the
Shift key temporarily reverses the Num Lock or non-Num-Lock
state of keys 71-73,75,77, and 79-83.
Ctrl
This key temporarily shifts keys 3, 7, 12, 14, 16-28, 30-38,
43-50,55,59-71,73,75,77,,79, and 81 to the Ctrl state. Also,
the Ctrl key used with the Alt and Del keys causes the system
reset function; with the Scroll Lock key, the break function; and
with the Num Lock key,the pause function. The system reset,
break, and pause functions are described in "Special Handling"
on the following pages.
83-Key Keyboard
4-9
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- Section 1. System Board
- 64/256K System Board
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