Apple Lisa - Keyboard; Keycodes

Confidential
Lisa Hardware Reference Manual
THE KEYBOARD
The keyboard connects to the computer through the jack on the lower
right front of the Lisa. Its 80 keys are fully programmable.
The keyboard
contains a microprocessor which scans the keys and
communicates the occurrence of a key depression or release to the
68000. The keyboard is a true N-key rollover design. An arbitrary
number of keys can be depressed without causing phantom key problems.
It is the responsibility of the 68000 side of the interface to
interpret key up and key doWn codes to properly handle functions such
as shift and auto-repeat. Any key can be programmed to generate an
NMl (non-maskable interrupt).
The keyboard's microprocessor contains an eight byte FIFO that
buffers keyboard data if the 68000 does not collect it fast enough.
Normally,
this FIFO keeps keycodes from being lost, but if the
keycodes are not read for a long enough time, the buffer will
eventually overflow and keycodes will be lost.
KEYCODES
Seven bits of the keycode byte identify the key which moved. The
other bit indicates whether the key went up or down. The key code
format
is:
drrr nnnn
If the d bit is 0, a key up transition has occurred. If it is 1,
a key down transition has occurred.
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