AN1775 Input Datasheet

AN1775 Datasheet, PDF, Equivalent


Part Number

AN1775

Description

Expanding Digital Input

Manufacture

Freescale Semiconductor

Total Page 12 Pages
Datasheet
Download AN1775 Datasheet


AN1775
www.DataSheet4U.com
Freescale Semiconductor
Order this document
by AN1775/D Rev. 1
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
For More Information On This Product,
Go to: www.freescale.com

AN1775
Application Note
Freescale Semiconductor, Inc.
Background
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.
Px0
Px1
Px2
Px3
Px4
Px5
Px6
Px7
Figure 1. Resistor Matrix Keypad Using Parallel Port Pins
For More Information On This Product,
Go to: www.freescale.com
AN1775 Rev. 1


Features www.DataSheet4U.com Freescale Semicondu ctor Order this document by AN1775/D R ev. 1 AN1775 Freescale Semiconductor, Inc... Expanding Digital Input with a n A/D Converter By Brad Bierschenk Free scale Applications Engineering Austin, Texas Introduction This application no te documents a method of extending digi tal input using the analog-to-digital c onverter (ADC) of a microcontroller uni t (MCU). Many MCU applications require digital input and arbitration. For exam ple, determining which key of a keypad was pressed. This is commonly done by a rranging switches in a matrix configura tion, connecting to a series of digital input pins, and reading a digital inpu t data register to determine which key was pressed. While this method is easil y implemented, it does require the use of an MCU’s parallel port pins. Some applications require all available bidi rectional or input-only pins for other purposes. In such a case, an alternate method of arbitrating keypresses is desired. By using the ADC of .
Keywords AN1775, datasheet, pdf, Freescale Semiconductor, Expanding, Digital, Input, N1775, 1775, 775, AN177, AN17, AN1, Equivalent, stock, pinout, distributor, price, schematic, inventory, databook, Electronic, Components, Parameters, parts, cross reference, chip, Semiconductor, circuit, Electric, manual, substitute




@ 2014 :: Datasheetspdf.com :: Semiconductors datasheet search & download site (Privacy Policy & Contact)