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PDF AN552 Data sheet ( Hoja de datos )
| Número de pieza | AN552 | |
| Descripción | Implementing Wake-up on Key Stroke | |
| Fabricantes | Microchip | |
| Logotipo |  |
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M
AN552
Implementing Wake-up on Key Stroke
Author:
Stan D’Souza
Microchip Technology Inc.
INTRODUCTION
Microchip's PIC16CXXX microcontroller family are ide-
ally suited to directly interface to a keypad. The high
4-bits of PORTB (RB7:RB4) have internal pull-ups and
can trigger a “change on state” interrupt. This interrupt,
if enabled, will wake the microcontroller from SLEEP. In
most battery powered applications, a microcontroller is
exercised when a key is pressed (e.g., in a remote key-
less entry system). The life of the battery can be
extended by using PIC16CXXX microcontrollers. This
is done by putting the PIC16CXXX microcontroller into
SLEEP mode for most of the time and wake-up only
when a key is pressed.
IMPLEMENTATION
Figure 1 depicts an application where four keys are
connected to RB7:RB4. Internal pull-ups are used to
maintain a high level on these inputs. In this example,
LEDs are connected to RB3:RB0. When SW1 is
pressed, LED1 is turned on and when SW2 is pressed,
LED2 is turned on and so on. The PIC16CXXX is
normally in SLEEP mode with the “change on state”
interrupt enabled. When SW1 is pressed, RB4 goes low
and triggers an interrupt. Since the PIC16CXXX is in
SLEEP, it first wakes up and starts executing code at
the interrupt vector. Note that if the global interrupt is
enabled, the program execution after an interrupt is at
the interrupt vector, if the global interrupt is not enabled,
the program starts executing the first line of code right
after the SLEEP instruction.
After waking up, a 20 - 40 ms de-bounce delay is
executed which checks the port for a key hit and,
depending on which key is hit, its associated LED is
turned on. The LEDs are used purely for demonstration
purposes. In a remote keyless entry application, the
remote code would be transmitted when the
appropriate key is hit.
Figure 2 depicts a 4x4 keypad interface to a
PIC16CXXX microcontroller. When using the
PIC16CXXX in a keypad application, the internal
pull-ups on RB7:RB4 can be enabled, eliminating the
need for external pull-up resistors. The series 100Ω
resistors are used for Electrostatic Discharge (ESD)
protection, and are recommended in keypad interface
applications.
SUMMARY
The PIC16CXXX is ideally suited to interface directly to
a keypad application. Built in pull-up resistors and very
low current consumption during sleep make it a very
good candidate for battery powered remote operations
and applications. Appendix A provides an example of
the code.
Performance:
Code Size -
RAM Used -
64 words
0 bytes
FIGURE 1:
4 KEY INTERFACE TO
PIC16CXXX
RB0
RB1
RB2
RB3
LED1
LED2
LED3
LED4
RB4
RB5
RB6
RB7
PIC16CXXX 4x100Ω
4x1k
SW1
SW2
SW3
SW4
FIGURE 2:
4x4 KEYPAD INTERFACE TO
PIC16CXXX
4x4
Key
Matrix
RB0
RB1
RB2
RB3
RB4
RB5
RB6
RB7
8x100Ω
PIC16CXXX
© 1997 Microchip Technology Inc.
DS00552E-page 1
Free Datasheet http://www.datasheetlist.com/
1 page  
Note the following details of the code protection feature on PICmicro® MCUs.
• The PICmicro family meets the specifications contained in the Microchip Data Sheet.
• Microchip believes that its family of PICmicro microcontrollers is one of the most secure products of its kind on the market today,
when used in the intended manner and under normal conditions.
• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowl-
edge, require using the PICmicro microcontroller in a manner outside the operating specifications contained in the data sheet.
The person doing so may be engaged in theft of intellectual property.
• Microchip is willing to work with the customer who is concerned about the integrity of their code.
• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable”.
• Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of
our product.
If you have any further questions about this matter, please contact the local sales office nearest to you.
Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
No representation or warranty is given and no liability is
assumed by Microchip Technology Incorporated with respect
to the accuracy or use of such information, or infringement of
patents or other intellectual property rights arising from such
use or otherwise. Use of Microchip’s products as critical com-
ponents in life support systems is not authorized except with
express written approval by Microchip. No licenses are con-
veyed, implicitly or otherwise, under any intellectual property
rights.
Trademarks
The Microchip name and logo, the Microchip logo, FilterLab,
KEELOQ, microID, MPLAB, PIC, PICmicro, PICMASTER,
PICSTART, PRO MATE, SEEVAL and The Embedded Control
Solutions Company are registered trademarks of Microchip Tech-
nology Incorporated in the U.S.A. and other countries.
dsPIC, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB,
In-Circuit Serial Programming, ICSP, ICEPIC, microPort,
Migratable Memory, MPASM, MPLIB, MPLINK, MPSIM,
MXDEV, PICC, PICDEM, PICDEM.net, rfPIC, Select Mode
and Total Endurance are trademarks of Microchip Technology
Incorporated in the U.S.A.
Serialized Quick Turn Programming (SQTP) is a service mark
of Microchip Technology Incorporated in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2002, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
2002 Microchip Technology Inc.
Microchip received QS-9000 quality system
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999. The
Company’s quality system processes and
procedures are QS-9000 compliant for its
PICmicro® 8-bit MCUs, KEELOQ® code hopping
devices, Serial EEPROMs and microperipheral
products. In addition, Microchip’s quality
system for the design and manufacture of
development systems is ISO 9001 certified.
Free Datasheet http://www.datasheetlist.com/
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet AN552.PDF ] | |
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