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UR5HCSPI-06 Datasheet (HTML) - Semtech Corporation

Part No. UR5HCSPI-06
Description  Zero-PowerTM Keyboard Encoder & Power Management IC for H/PCs
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Maker  SEMTECH [Semtech Corporation]
Homepage  http://www.semtech.com
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 6 page
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“GHOST” KEYS
KEYBOARD SCANNER
Copyright Semtech 1997-2001
DOC5-SPI-06-DS-103
www.semtech.com
6
The encoder scans a keyboard organized as an 8 row by 14 column matrix
for a maximum of 112 keys. Smaller size matrixes can also be
accommodated by simply leaving unused pins open. The UR5HCSPI-06
provides internal pull-ups for the Row input pins. When active, the encoder
selects one of the column lines (C0-C13) every 512 µS and then reads the
row data lines (R0-R7). A key closure is detected as a zero in the
corresponding position of the matrix.
A complete scan cycle for the entire keyboard takes approximately 9.2 mS.
Each key found pressed is debounced for a period of 20 mS. Once the key
is verified, the corresponding key code(s) are loaded into the transmit buffer
of the SPI communication channel.
N-Key Rollover
In this mode, the code(s) corresponding to each key press are transmitted
to the host system as soon as that key is debounced, independent of the
release of other keys.
When a key is released, the corresponding break code is transmitted to the
host system. There is no limitation to the number of keys that can be held
pressed at the same time. However, two or more key closures, occurring
within a time interval of less than 5mS, will set an error flag and will not be
processed. This feature is to protect against the effects of accidental key
presses.
Data Command Buffer
The UR5HCSPI-06 implements a data buffer, which contains the key
code/command bytes waiting to be transmitted to the host. If the data
buffer is full, the whole buffer will be cleared and an "Initialize" command will
be sent to the host. At the same time, the keyboard will be disabled until
the "Initialize" or "Initialize Complete" command from the host is received.
Power Management Unit
In most keyboard subsystems, the power consumption is determined by the
use of the LEDs. In these situations, USAR has implemeneted two modes
of operation to minimize power drain. (For more information, see page 10
on the UR5HCSPI datasheet - doc5-spi-ds-100.pdf.) However, since the
SPICoderTM 06 does not provide LED ouput/input, this is not a concern.
In any scanned contact switch matrix,
whenever three keys defining a
rectangle on the switch matrix are
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.
Figure 1: “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 should be placed in the
same row or column of the matrix,
whenever possible. Shift Keys (Shift,
Alt, Ctrl, Window) should not reside in
the same row (or column) as any
other keys. The UR5HCSPI-06 has
built-in mechanisms to detect the
presence of “ghost” keys.
Actual key presses
“Ghost”
Key



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