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AN1775 Datasheet(PDF) 2 Page - Freescale Semiconductor, Inc

Part No. AN1775
Description  Expanding Digital Input with an A/D Converter
Download  12 Pages
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Maker  FREESCALE [Freescale Semiconductor, Inc]
Homepage  http://www.freescale.com

AN1775 Datasheet(HTML) 2 Page - Freescale Semiconductor, Inc

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Application Note
AN1775 Rev. 1
Dedicated Input
A microcontroller typically receives user input through digital input pins.
The simplest implementation is a single switch directly connected to a
digital input pin. This is easy to realize, but is not the most efficient use
of resources, with one pin dedicated to one input. One port data bit
represents the state of one switch.
Matrix Input
Another method uses a keypad, a common element in embedded
systems. These are ordinarily arranged in a matrix, as shown in
Figure 1
. In this case, the byte value of an entire port data register can
be polled to determine which key was pressed. This is more efficient, as
a 4 x 4 keypad can interface 16 keys with eight input pins.
Figure 1. Resistor Matrix Keypad Using Parallel Port Pins
P x 0
P x 1
P x 2
P x 3
P x 4
P x 5
P x 6
P x 7
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com

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