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Appendix C Keyboard
C.2.4 KEYS
All keys generate a Make code (when pressed) and a Break code (when released) with the
exception of the Pause key (pos. 16), which produces a Make code only. All keys with the
exception of the Pause and Easy Access keys are also typematic, although the typematic action
of the Shift, Ctrl, Alt, Num Lock, Scroll Lock, Caps Lock, and Ins keys is suppressed by the
BIOS. Typematic keys, when held down longer than 500 ms, send the Make code repetitively at a
10-12 Hz rate until the key is released. If more than one key is held down, the last key pressed
will be typematic.
C.2.4.1 Special Single-Keystroke Functions
The following keys provide the intended function in most applications and environments.
Caps Lock - The Caps Lock key (pos. 59), when pressed and released, invokes a BIOS
routine that turns on the caps lock LED and shifts into upper case key positions 40-49, 60-68,
and 76-82. When pressed and released again, these keys revert to the lower case state and the
LED is turned off. Use of the Shift key will reverse which state these keys are in based on the
Caps Lock key.
Num Lock - The Num Lock key (pos. 32), when pressed and released, invokes a BIOS routine
that turns on the num lock LED and shifts into upper case key positions 55-57, 72-74, 88-90,
100, and 101. When pressed and released again, these keys revert to the lower case state and the
LED is turned off.
The following keys provide special functions that require specific support by the application.
Print Scrn - The Print Scrn (pos. 14) key can, when pressed, generate an interrupt that initiates
a print routine. This function may be inhibited by the application.
Scroll Lock - The Scroll Lock key (pos. 15) when pressed and released, invokes a BIOS
routine that turns on the scroll lock LED and inhibits movement of the cursor. When pressed and
released again, the LED is turned off and the function is removed. This keystroke is always
serviced by the BIOS (as indicated by the LED) but may be inhibited or ignored by the
application.
Pause - The Pause (pos. 16) key, when pressed, can be used to cause the keyboard interrupt to
loop, i.e., wait for another key to be pressed. This can be used to momentarily suspend an
operation. The key that is pressed to resume operation is discarded. This function may be ignored
by the application.
The Esc, Fn (function), Insert, Home, Page Up/Down, Delete, and End keys operate at the
discretion of the application software.
hp/Compaq Personal Computers
Changed - April 2003
C-8