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AN1775: Descriptionexpanding digital input with an A/D converter; File Size377KB，12 Pages; ManufacturerFREESCALE (NXP)

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expanding digital input with an A/D converter

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Freescale Semiconductor

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by AN1775/D Rev. 1

AN1775

Freescale Semiconductor, Inc...

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.

AN1775 Rev. 1

For More Information On This Product,

Go to: www.freescale.com

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