LIMITATIONS
OF
THE
KEYBOARD
The Amiga keyboard
(see
figure
8-3)
is a matrix of rows and columns, with a key switch
at
each intersection. Because of this, it
is
subject to a phenomenon called "ghosting."
Ghosting means
that
certain combinations of keys pressed simultaneously will cause
extra ("ghost") key codes
to
be
transmitted. For example, press "A" and "S" simultane-
ously and hold them down. Notice
that
"A" and "S" are transmitted. While still hold-
ing them down, press "Z" and observe
that
both "X" and "Z" are transmitted. In this
case, "X" is a ghost key.
The keyboard is designed so
that
this will never happen during normal typing, only
when unusual key combinations like the one
just
described are pressed. Normally, the
keyboard will appear
to
have "N-key rollover," which means
that
you will run out of
fingers before generating a ghost character.
ESC
45
00
TAB
CTRL
63
SHIFT
NOTE
There are seven keys
that
are not
part
of the matrix, and thus do not contri-
bute
to
generating ghosts. These keys are: CTRL (control), the two SHIFT
keys, the two Amiga keys, and the two ALT keys.
Fl
1 8
3D
3E
HELP 4
5
20
2E
1 2
10
1E
0
31
OF
A
.it
ALT
ENTER
9
3F
6
2F
3
1F
3C
64
66
40
67
4A
43
Figure
8-3:
The Amiga Keyboard, Showing Keycodes in Hexadecimal
Interface Hardware
239
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