AN1775 Datasheet, PDF (1/12 Pages) Freescale Semiconductor, Inc – Expanding Digital Input with an A/D Converter

Freescale Semiconductor
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AN1775
Expanding Digital Input with an A/D Converter
By Brad Bierschenk
Freescale Applications Engineering
Austin, Texas
Introduction
This application note documents a method of extending digital input
using the analog-to-digital converter (ADC) of a microcontroller unit
(MCU).
Many MCU applications require digital input and arbitration. For
example, determining which key of a keypad was pressed. This is
commonly done by arranging switches in a matrix configuration,
connecting to a series of digital input pins, and reading a digital input
data register to determine which key was pressed. While this method is
easily implemented, it does require the use of an MCU’s parallel port
pins.
Some applications require all available bidirectional or input-only pins for
other purposes. In such a case, an alternate method of arbitrating
keypresses is desired. By using the ADC of an MCU connected to a
resistor ladder, user input can be more efficiently processed.
© Freescale Semiconductor, Inc., 2004. All rights reserved.
© Motorola, Inc., 1998
AN1775 Rev. 1
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