UR5HCFJL Datasheet, PDF (4/20 Pages) Semtech Corporation – Zero-PowerTM Keyboard Encoder for Portable Systems

KEYBOARD ENCODER, (CON’T)
Embedded Numeric Keypad
MODE CONTROL
N-Key Rollover
The GreenCoder^TM implements an
embedded numeric keypad. The
Numeric Keypad Function is
invoked by pressing the Num Lock
Key.
FN Key
A special FN Key has been
implemented to perform the
following functions while it is held
pressed:
• Function Key F1 becomes F11
• Function Key F2 becomes F12
• Control Left Key becomes Ctrl
Right
• Embedded numeric keypad keys
become regular keys
If Num Lock is not set:
• Embedded numeric keypad keys
provide the same codes as a
numeric keypad when the Num
Lock is not set (Arrow keys, PgUp,
PgDn, etc.)
Status LED indicators
The controller provides an interface
for three LED shift status indicators.
All three pins are active low to
indicate the status of the host
system (Num Lock, Caps Lock and
Scroll Lock) and are set by the
system. After approximately a one-
minute period of keyboard inactivity,
LEDs are dimmed to conserve
power. They are set to full
brightness again upon a new
keystroke.
In this mode, the code(s) corresponding to each key press are transmitted
to the host system as soon as that key is debounced, independently of the
release of other keys.
If a key is defined to be Typematic, the corresponding make code(s) will be
transmitted while the key is held pressed. When a key is released, the
corresponding break code(s) are then transmitted to the host system. If the
released key happens to be the most recently pressed, then Typematic
action is terminated. There is no limitation in the number of keys that can
be held pressed at the same time. However, two or more key closures,
occurring within a time interval less than 5 mS, will set an error flag and will
not be processed. This procedure protects against effects of accidental key
presses.
“Ghost” Keys
In any scanned contact switch matrix, whenever three keys defining a
rectangle on the switch matrix are held pressed at the same time, a fourth
key positioned on the fourth corner of the rectangle is sensed as being
pressed. This is known as the “ghost” or “phantom” key problem. Although
the problem cannot be totally eliminated without using external hardware,
there are methods to neutralize its negative effects for most practical
applications. Keys that are intended to
be used in combinations or are likely to
Actual key presses
be pressed at the same time by a fast
typist (i.e., keys located in adjacent
positions on the keyboard) should be
placed in the same row or column of the
matrix whenever possible. Shift Keys
“Ghost”
(Shift, Alt, Ctrl) should not reside in the
Key
same row (or column) with any other
keys. The GreenCoder^TM has built-in
mechanisms to detect the presence of a
“ghost” key, thus eliminating the
necessity of external hardware.
Figure 1: “Ghost” or “Phantom” Key
Problem
Copyright Semtech, 1997-2001
4
DOC5-FJL-DS-106
www.semtech.com