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Platforms
©2000-2008 Tibbo Technology Inc.
Details
For internal housekeeping reasons, the total size of the disk as returned by this
property may be less than the size that was requested when formatting the disk
with the
method. Actual usable capacity (
) of the disk is
less because the disk also needs a number of sectors for its "housekeeping" data
(see
).
) for this property to return a
meaningful value.
Kp Object
This is the keypad (kp.) object, it allows you to work with a "matrix" keypad of up
to 64 keys (8 scan lines by 8 return lines).
Features:
. Scan lines can double as LED control lines too.
for each key allow you to create sophisticated keypad
input. Individual programming of
for each state transition.
for scan and return lines -- use any I/O lines, in any order.
Ability to
the keypad when a certain key event/code combination
is encountered.
8.3.14.1
Possible Keypad Configurations
The kp object works with a "matrix" keypad formed by scan and return lines. The
keypad object supports up to 8 scan and 8 return lines, which means that you can
build a keypad with up to 64 keys. A sample schematic diagram for a typical
keypad is shown below.
During the scanning process, the kp object "activates" one scan line after another.
The line is activated by setting it LOW, while keeping all other scan lines HIGH. For
each scan line, the kp object samples the state of return lines. If any return line is
at LOW, this means the key located at the intersection of this return line and the
currently active scan line is pressed.
A detailed discussion of the schematics falls outside the scope of this manual. We
will only notice, in passing, that the diodes D1-D4 are necessary and should not be
omitted. For best result, use Schottky diodes -- they have low drop voltage. Pull-
up resistors R1-R4 prevent the return lines from floating and should be present as
well.
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