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AN1024PKE System Design Using the PIC16F639

INTRODUCTIONHands-free Passive Keyless Entry (PKE) is quicklybecoming mainstream in automotive remote keylessentry applications and is a common option on newautomobile models. Instead of pressing a transmitterbutton to unlock or lock a car door, it is possible to gainvehicle access simply having a valid transponder inyour possession.

Hands-free PKE applications require bidirectionalcommunication between the base station andtransponder units. The base unit inside the vehicletransmits a Low-Frequency (LF) command thatsearches for a transponder in the field. Once located,the transponder in the vehicle owner’s possession thenautomatically responds to the base unit. The base unitthen unlocks the car doors, if a valid authenticationresponse is received.

In typical PKE applications, the base station unit isdesigned to output the maximum power that is allowedby electromagnetic field radiation rules that aremandated by government agencies. When it operateswith a 9 to 12 VDC of power source, the maximumattainable antenna voltage is about 300 VPP. Becauseof the non-propagating property of the low-frequency(125 kHz) signal, the signal level becomes only abouta few mVPP when it is received by a typical key fobtransponder approximately two meters away from the

base station unit. Furthermore, due to antennaorientation properties, the input signal level at thetransponder becomes considerably weaker if theantenna is not oriented face-to-face with the basestation antenna.

The most probable source of PKE operation failure isdue to a weak input signal level at the transponder.Therefore, for a reliable hands-free PKE application, itis necessary to make the input signal strong enough(above input sensitivity level) in any condition within thedesired communication range.

In order to make the PKE system reliable, the systemdesigner must consider four important parameters:

1. Output power of the base station command,2. Input sensitivity of the transponder,3. Antenna directionality, and 4. Battery life of the transponder.

The PIC16F639 is a microcontroller (MCU) with athree-channel analog front-end. The device’s analogfront-end features are controlled by the MCU firmware.Because of its easy-to-use features, the device can beused for various smart low-frequency sensing andbidirectional communication applications.

This application note provides design circuit examplesof the smart PKE transponder using the PIC16F639MCU. The MCU firmware examples for the circuitsshown in this application note are also available. Thegiven circuit and MCU firmware examples can be easilymodified for users specific applications.

Author: Youbok Lee, Ph.D.Microchip Technology Inc.

© 2007 Microchip Technology Inc. DS01024B-page 1

AN1024

PIC16F639 PKE TRANSPONDERThe PIC16F639 has a digital MCU section (PIC16F639core) and an analog front-end (AFE) section. Thedevice can be used for various low-frequency sensingand bidirectional smart communication applications.

Figure 1 shows an example of a typical PKE system.The base station unit transmits a 125 kHz command tosearch for a valid transponder in the field. The PKEtransponder sends back a response if the receivedcommand is valid.

The PIC16F639 device has high analog inputsensitivity (up to 1 mVPP) and three antennaconnection pins. By connecting three antennas that arepositioned to x, y and z directions, the transponder canpick up signals from any direction at any given time.Therefore, it reduces the likelihood of missing signalsdue to the properties of antenna directionality. Theinput signal at each antenna pin is detectedindependently and summed afterwards. Each inputchannel can be independently enabled or disabled byprogramming the Configuration register. The deviceconsumes less operating power if fewer channels areenabled.

For hands-free operation, the transponder is continu-ously waiting and detecting input signals. This presentsan issue for the life expectancy of the battery. There-fore, in order to reduce the operating current, the digitalMCU section can stay in low-current mode (Sleep),while the Analog Front-End (AFE) is looking for a validinput signal. The digital MCU section is waking up onlywhen the AFE detects a valid input signal. This featureis possible by using an Output Enable Filter (wake-upfilter). There are nine Output Enable Filter optionsavailable in the PIC16F639. Users can program thefilter using the Configuration register. Once the filter isprogrammed, the device passes detected output to thedigital section only if the incoming signal meets the filterrequirement.

Figure 2 shows an example of the PKE transponderconfiguration. The transponder consists of thePIC16F639 device, external LC resonant circuits, pushbuttons, a UHF transmitter, battery back-up (optional),and a 3V lithium battery.

The digital sections have two I/O ports; PORTA andPORTC. Each of the PORTA pins is individuallyconfigurable as an Interrupt-on-change pin. The pinson PORTC have no Interrupt-on-change function.

The AFE section shares three I/O pins in PORTC of thedigital section; RC1, RC2 and RC3, which are internallybonded with CS, SCLK/ALERT and LFDATA/CCLK/RSSI/SDIO pad of the AFE, respectively. LFDATA/CCLK/RRSI and ALERT are outputs of the AFE. SDIO,SCLK and CS are used to program or read the AFEConfiguration registers. Refer to the PIC12F635/PIC16F636/639 Device Data Sheet (DS41232) for moredetails (see “References”).

To save battery power, the digital section is normally inSleep mode while the AFE section is detecting LF inputsignals. Although the AFE’s output pads are internallybonded to the PORTC pins, the AFE output cannotwake-up the digital section from Sleep by Interrupt-on-change events, because the pins are not Interrupt-on-change pins. Therefore, it is recommended that theLFDATA and ALERT pins of the AFE be connected tothe PORTA pins externally, as shown in Figure 2.

The digital section can wake up when one of thefollowing three conditions occur:

1. AFE output at LFDATA pin,2. AFE output at ALERT pin, or3. Any event by push button switches on PORTA.

DS01024B-page 2 © 2007 Microchip Technology Inc.

AN1024
FIGURE 1: BIDIRECTIONAL PASSIVE KEYLESS ENTRY (PKE) SYSTEM
FIGURE 2: EXAMPLE OF PASSIVE KEYLESS ENTRY (PKE) TRANSPONDER CONFIGURATION

LED

UHFTransmitter

3-InputAnalog Front-End

MCU (PIC16F636)

+

PIC16F639

LED

UHFReceiver

LFTransmitter/

Receiver

Mic

roco

ntro

ller

(MC

U)

LF Command(125 kHz)

LF Talk-back(125 kHz)

Response(UHF)

EncryptedCodes

Base Station Transponder

Ant. X

Ant. Y

Ant. Z

125 kHzLC SeriesResonant Circuit

125 kHzLC ParallelResonant Circuit

(MCP2030)

PIC

16F6

39

1

2

3

4

20

19

18

17

5

6

7

16

15

14

8

9

10

13

12

11

+3V+3V

VDD

S0

S1

S2

S3

S4

S5

VSS

Data

RFEN

LFDATA/RSSI/SDIOVDDT

LCZ

LCY

CS

SCLK/ALERT

VSST

LED

LCCOM

LCX

RF Circuitry(UHF TX)

433.92 MHz

air-corecoil ferrite-core

coilferrite-core

coil

Battery(2-3.6V) D1

D2

C1D3

D4

Push Button Switch


AN1024
Wake-up Filter and Signal DetectionUsers can program one of the nine possible OutputEnable filters using the Configuration registers. Refer tothe PIC12F635/PIC16F636/639 Device Data Sheet(DS41232) for more details (see “References”).
Figures 3 and 4 show examples of inputs anddemodulated outputs. The input signal is applied to oneof the three input pins or on all pins (LCX, LCY, LCZ) atthe same time. The outputs are available on theLFDATA pin of the device. The figures show thedifferences in output pins depending on the setting ofthe output enable (wake-up) filter option. For the casesshown in Figure 3 and Figure 4, the minimum

modulation depth requirement is set to 8% and theOutput Enable Filter is set to (TOEH: 2 ms, TOEL = 2 ms).The input signal amplitude is 2.7 mVPP with amodulation depth of about 9%. Figure 3 shows theinput signal and the demodulated data output after thewake-up filter is matched. The demodulated output ofthe correct (wanted) input signal wakes up the digitalsection, and will respond if the command is valid.Figure 4 shows the case when the input does not meetthe programmed filter requirement. The demodulatedoutput is not available at the output pin since the inputdoes not meet the programmed filter requirement. Thisensures that the digital section will not wake-up due tounwanted input signals.

FIGURE 3: INPUT SIGNAL AND DEMODULATED OUTPUT WHEN OUTPUT ENABLE FILTER IS ENABLED AND INPUT MEETS THE FILTER TIMING REQUIREMENT

FIGURE 4: INPUT SIGNAL AND DEMODULATED OUTPUT WHEN OUTPUT ENABLE FILTER IS ENABLED AND INPUT DOES NOT MEET THE FILTER TIMING REQUIREMENT


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External LC Resonant AntennaThe PIC16F639 device includes three low-frequencyinput channels. The LCX, LCY and LCZ pins are forexternal LC resonant antenna circuit connections (foreach LF input channel). The external circuits are con-nected to the antenna input pins and the LCCOM pin.LCCOM is a common pin for all external antenna cir-cuits. A capacitor (1-10 μF) between the LCCOM pinand ground is recommended to provide a stable condi-tion for the internal detection circuit when it detectsstrong input signals.
Although the PIC16F639 has three LC input pins for thethree external antenna attachments, the user can useonly one or two antennas, instead of using all three,depending on the application. The operating currentconsumption is proportional to the number of channelsenabled. Fewer channels enabled results in lowercurrent consumption. However, it is highlyrecommended to use all three antennas for hands-freePKE applications.

THEORY OF LC RESONANT ANTENNATo detect a low-frequency magnetic field, a tuned loopantenna is commonly used. In order to maximize theantenna voltage, the loop antenna must be preciselytuned to the frequency of interest. For PKEapplications, the antenna should be tuned to the carrierfrequency of the base station. The loop antenna ismade of a coil (inductor) and capacitors that areforming a parallel LC resonant circuit. The voltageacross the antenna is also maximized by increasing thesurface area of the loop and quality factor (Q) of thecircuit.

The resonant frequency of the LC resonant circuit isgiven by Equation 1:

EQUATION 1:

where L is the inductance of the loop and C is thecapacitance.

For a given LC resonant circuit, the received antennavoltage is approximately given by Equation 2 (refer toapplication note AN710, “Antenna Circuit Design forRFID Applications,” (DS00710) for details):

EQUATION 2:

where:

In Equation 2, the quality factor (Q) is a measure of theselectivity of the frequency of the interest by the tunedcircuit. Assuming that the capacitor is lossless at125 kHz, Q of the LC circuit is mostly governed by theinductor defined by:

EQUATION 3:

where fo is the tuned frequency, L is the inductancevalue and r is the resistance value of the inductor.

In typical transponder applications, the inductancevalue is in the 1-9 mH range. Q of the LC circuit isgreater than 20 for an air-core inductor and about 40 fora ferrite-core inductor.

The S cos α term in Equation 2 represents an effectivesurface area of the antenna that is defined as anexposed area of the loop to the incoming magneticfield. The effective antenna surface area is maximizedwhen cos α becomes unity, which occurs when theantennas of the base station and the transponder unitsare positioned in a face-to-face arrangement. Inpractical applications, the user might notice the longestdetection range when the two antennas are facing eachother and the shortest range when they areorthogonally faced. Figure 5 shows a graphicaldemonstration of the antenna orientation problem inpractical applications.

fo1

2π LC------------------=

fc = Carrier frequency of the base station (Hz)

Δ f = | fc - fo| fo = Resonant frequency of LC circuit (Hz)

N = Number of turns of coil in the loop

S = Surface area of loop in square meters

Q = Quality factor of LC circuit

Βo = Magnetic field strength (Weber/m2)

α = Angle of arrival of signal

Vcoil fc

1 Δf+( )-------------------NSQBo αcos≈

QL2π fo L

r----------------------=


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FIGURE 5: ANTENNA ORIENTATION
DEPENDENCY

The antenna orientation problem can be significantlyreduced if the three antennas are placed orthogonallyon the same PCB board. This increases the probabilitythat at least one of the transponder antennas facestoward the base station antenna at a given incidentduring application. Figure 6 shows a graphicalillustration of placing three antennas on thetransponder board. A large air-core coil is used for LCZand two ferrite-core coils are used for LCX and LCY.There are companies that make the ferrite coilsspecifically for the 125 kHz RFID and low-frequencysensing applications.

FIGURE 6: RECOMMENDED ANTENNA PLACEMENT ON TRANSPONDER BOARD

Transponder’s LF antenna

Magnetic field from the base station

a

Line of axis

Effective Antenna Surface Area = S cos a

with surface area S

Transponder PCB

Ferrite-core Antenna

(LCY Input Pin)

(LCZ antenna)

(LCX Input Pin)

Ferrite-core Antenna

Air-core Antenna

Note 1: Keep the size of the air-core antenna (LCZ)as large as possible, given the PCB spaceavailable.

2: Keep the separation between the antennasas far apart as possible to reduce a mutualcoupling between them.


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LC ANTENNA TUNINGAs shown in Equations 2 and 3, the induced coil volt-age is maximized when the LC circuit is tuned preciselyto the incoming carrier frequency. In practical applica-tions, however, the LC resonant frequency differs fromtransponder to transponder due to the tolerance varia-tion of the LC components. To compensate the errordue to the component tolerance, the PIC16F639 hasan internal resonant capacitor bank per channel. Thecapacitor value can be programmed up to 63 pF with1 pF per step. Figure 7 shows an example of thecapacitance tuning using the Configuration register bits(6 bits). The capacitance is monotonically increasedwith the Configuration register bits. Refer to thePIC12F635/PIC16F636/639 Device Data Sheet(DS41232) for more details (see “References”).
The capacitance can be effectively tuned by monitoringthe RSSI current output. The RSSI output is propor-tional to the input signal strength. Therefore, the higherRSSI output will be monitored the closer the LC circuitis tuned to the carrier frequency.

The total capacitance adds up as the Configurationregister bits step up . The resulting internal capacitanceis added to the present capacitor values of the LCcircuit. The LC resonant frequency will shift to lower byadding the internal resonant capacitor.

FIGURE 7: CAPACITANCE TUNING VS. BIT SETTING

Battery Back-up and Batteryless ModesIn real-life applications, there is the chance that thebattery can be momentarily disconnected from thecircuit by accident, for example, if the unit is droppedonto a hard surface. If this should happen, the datastored in the MCU may not be recovered correctly. Toprotect the battery from accidental misplacement,users may consider using a battery back-up circuit. Thebattery back-up circuit provides a temporary VDDvoltage to the transponder. The circuit is recommendedfor sophisticated transponders, but may not be anecessary mechanism for all applications. In Figure 2,D4 and C1 form the battery back-up circuit. C1 is fullycharged when the battery is connected and providesthe VDD when the battery is momentarily disconnected.

The Batteryless mode is the case when the transpon-der is operating without the battery. In Figure 2, diodesD1, D2, D3 and C1 form a power-up circuit for battery-less operation. When the transponder coil developsvoltages, the coil current flows through the diodes, D1and D2, and charges the capacitor, C1, which can pro-vide the VDD for the transponder. The power-up circuitis useful when the PIC16F639 is used for anti-collisiontransponder applications, where batteryless operationis preferred. The value of the capacitor, C1, for Battery-less mode is from a few μF to a few Farad (F)depending on the application.

0

10

20

30

40

50

60

70

0 20 40 60 80

Bit Setting (steps)

Cap

acita

nce

(pF)

Ch. XCh. YCh. Z


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LOW-FREQUENCY SIGNAL DETECTION ALGORITHM AND DETECTOR OUTPUTFigure 8 shows the flow chart of the input signal detec-tion with the wake-up filter enabled.

The MCU firmware, PIC16F639_Basestation.asm, isavailable for download from Microchip’s web site,www.microchip.com (see Appendix A: “SourceCode”).

Examples of the schematics for the PKE transponderand the base station are shown in Appendix B:“Transponder”, Figure B-1, Figure C-1 and Figure C-2respectively. These schematics were developed forcustomer training purposes of the PIC16F639transponder. Users can use the circuits as referenceswhen they develop their own systems. Users can alsorefer to the PKE reference demonstration kit (P/N: APGRD001), which is available from Microchip.

FIGURE 8: PIC16F639 SIGNAL DETECTION FLOW CHART

Start

Input Signal in?

Set AGC Active Status bit(if AGC is on)

Set Input Channel ReceivingStatus bit (CH X, Y or Z)

Wake-up FilterEnabled?

Input SignalDisappeared for

> 16 ms?

Input SignalMeets Wake-up Filter

Requirements?

No

Yes

Set ALERT Output Pin Low

Set Alarm Status Bit High(If ALRTIND Bit is Set)

No

YesSoft Reset

Detected Output on LFDATA Pin (LFDATA output wakes up MCU)

Yes

Yes

No

No Input Signal Continuesfor > 32 ms?

MCU Programs AFEConfiguration Registers

MCU in Sleep Mode(while AFE detects input signals)

No

Yes

Correct Data?

Send Response viaLF Talk-back or RF Link

Yes

No

= Controlled by MCU Firmware

Incorrect


AN1024

TRANSPONDER CIRCUITFigure B-1, in Appendix B: “Transponder”, shows anexample of the PKE transponder circuit which has beenused for customer training and device demonstrationpurposes.

The transponder circuit has three external LC resonantcircuits, 5 push button switches, a 433.92 MHzresonator for UHF data transmission and componentsfor Battery Back-up mode.

Each LC resonant circuit is connected to the LC inputand LCCOM pins. The air coil antenna is connected tothe LCX input and the two ferrite-rod inductors areconnected to the LCY and LCZ pins. The LCCOM pinis a common pin for all three antenna connections,which is grounded via C11 and R9. Each resonantantenna must be tuned to the carrier frequency of thebase station unit for the best signal receptionconditions. The internal capacitor of each channel canbe used to tune the antenna for the best performance.

When the device is powered up initially, the digitalsection programs the Configuration registers of theAFE using the SPI (CS, SCLK/ALERT, SDIO).

The AFE is very sensitive to environmental noise dueto its high input sensitivity (~3 mVPP); therefore, takeappropriate care to prevent excess AC noise along thePCB traces. Capacitors C6 and C12 are used for noisefiltering for the VDD and VDDT pins, respectively.

Diodes D1 and D2, and capacitor C5 are for the BatteryBack-up mode. Diodes D2, D3 and D7 and capacitorC5 are for Batteryless mode. A larger C5 value isneeded for stable Batteryless mode operation. Capac-itor C5 holds the charges from the battery and from thecoil voltage through diodes D3 and D7. The storedcharge on C5 can keep the PIC16F639 device pow-ered when the battery is momentarily disconnected.Diodes D3 and D7 are connected across the air coil,which develops the strongest coil voltage among thethree external LC resonant antennas.

Once a valid input signal is detected, the digital MCUsection is waken up and transmits a response if thecommand is valid.

The transponder can send responses using an internalmodulator (LF talk-back) or an external UHFtransmitter. The analog input channel has an internalmodulator (transistor) per channel between the inputand the LCCOM pins. The internal modulator is turnedon and off if the AFE receives Clamp-On and Clamp-Off commands from the digital MCU section,respectively. The antenna voltage is clamped orunclamped depending upon the Clamp-On or Clamp-Off command, respectively. This is called LF talk-back,which is used for proximity range applications only. Thebase station can detect the changes in the transponderantenna voltage and reconstruct the modulation data.

See the PIC12F635/PIC16F636/639 Device DataSheet (DS41232) for more details of the LF talk-back(see “References”).

The transponder uses a UHF transmitter for long rangeapplications. An On-Off-Keying UHF transmitter isformed by the UHF (433.92 MHz) resonator U2 andpower amplifier Q1. The values of capacitors C2 andC3 are approximately 20 pF range each, but are layoutdependent. The L1, which is typically formed by a metaltrace on the PCB, is a UHF antenna and its efficiencyincreases significantly by increasing its loop area.

The UHF transmitter section is turned on when theMCU I/O pin outputs a logic level high; otherwise it isturned off. The output of RC5 is the modulation data ofthe UHF signal and can be reconstructed by the UHFreceiver in the base station.


AN1024
BASE STATION CIRCUITFigure C-1 and Figure C-2, in Appendix C: “BaseStation”, show an example circuit of the base station,which has been used for customer training and devicedemonstration purposes.
The base station unit consists of a microcontroller,125 kHz transmitter/receiver and an UHF receivermodule.

The base station transmits a 125 kHz low-frequencycommand and receives responses from thetransponders in the field via UHF or LF talk-back. Aftertransmitting the LF commands, it checks whether thereis any response through LF or UHF link.

The 125 kHz transmitter generates a carrier signalbased on the MCU’s Pulse-Width Modulator (PWM)output. The power of the125 kHz square pulses fromthe MCU is boosted by the current driver, U1. Thesquare pulse output from U1 becomes sine waves as itpasses through an LC series resonant circuit that isformed by L1, C2, C3 and C4. L1 is an air-core inductorand is used for the 125 kHz LF antenna.

The antenna radiation becomes maximized when theLC series resonant circuit is tuned to the frequency ofthe PWM signal. At the resonant frequency, theimpedance of the LC circuit is minimized. This resultsin a maximum load current through L1 and thereforeproduces strong magnetic fields. Users may tune theLC circuit by monitoring the coil voltage across L1.

The components after diode D1 are used to receive theLF talk-back signal from the transponder. When thetransponder responds with LF talk-back, there will bechanges in the coil voltage (across L1) due to the mag-netic fields originated by the voltage on the transpondercoil. Since the voltage on the transponder coil is initiallycaused by the voltage of the base station antenna (L1),the return voltage has 180º phase difference withrespect to the originating voltage. Therefore, at a givencondition, the voltage across L1 changes with the coilvoltage of the transponder coil.

The change in the coil voltage (across L1) can bedetected through an envelope detector and low-passfilter formed by D1 and C5. The detected envelopepasses through active gain filters, U2A and U2B. Thedemodulated analog output is fed into the comparatorinput pin of the MCU for pulse shaping. The output ofthe comparator is available on TP6 and decoded by theMCU.

U4 is the 433.92 MHz ASK receiver module. Thisreceiver module detects the transponder’s UHFresponses. The digital output from this module is fedinto the MCU for decoding. An antenna (a few incheslong) is typically attached to the antenna pad of themodule to receive a signal in stable condition. Since thereceiver module is next to the LF transmitter section,which produces strong fields, the module typicallyoutputs noise. Therefore, it may require an adequatefirmware routine to filter out the noise inputs.

The base station unit displays the data on the LCD orturns on the buzzer each time valid data is received.

FIRMWARE EXAMPLESFirmware examples, including HTML documentationfor the transponder and the base station units are avail-able in an archived file (see Appendix A: “SourceCode”).

The main firmware files for the transponder and thebase station are PIC16F639_Transponder.asm andPIC16F639_BaseStation.asm, respectively.

The firmware does not use the KEELOQ® security ICalgorithm. Contact Microchip sales for assistance if youwant to use KEELOQ security ICs in your design.

Figure 9 shows an example of the handshake betweenthe base station and the transponder.

Figure 10 shows a communication example betweenthe transponder and base station units by using thefirmware.

FIGURE 9: EXAMPLE OF HANDSHAKE BETWEEN BASE STATION AND TRANSPONDER

Base Station Transmits:(Step 1)

AGC Stabilization Pulse + Wake-up Filter + 10 bits (ID Command + Parity + Stop Bit)

Transponder Transmits:(Step 2)

Header + ID (32 bits) + 4 Parity bits

Base Station Transmits:(Step 3)

AGC Stabilization Pulse + Wake-up Filter + IFF Command (8 bits) +Challenge (32 bits) + 5 Parity bits + Stop Bit (46 bits)

Transponder Transmits:(Step 4)

Header + Response (32 bits) + 4 Parity bits (36 bits)

Base Station: Display message on LCD


AN1024
FIGURE 10: COMMUNICATION LINK BETWEEN BASE STATION AND TRANSPONDER
CONCLUSIONThe PIC16F639 device is an easy-to-use, low cost andsecure bidirectional communication transponder. Thisdevice can be used for various smart hands-freepassive keyless entry applications. A basic configura-tion of the Passive Keyless Entry (PKE) transponder isshown in Figure 2. Example schematics for the tran-sponder and the base station are shown in AppendixB: “Transponder” and Appendix C: “Base Station”.

The firmware examples for the transponder and thebase station are also provided (see Appendix A:“Source Code”). Users can modify the providedexamples for their application purposes.

MEMORY USAGE

Transponder:• Program Memory – 1131 words• Data Memory – 65 Bytes

Base Station:• Program Memory – 1178 words• Data Memory – 405 Bytes

REFERENCES“PIC12F635/PIC16F636/639 Data Sheet,” DS41232,Microchip Technology Inc.

AN710, “Antenna Circuit Design for RFIDApplications,” Application Note (DS00710), MicrochipTechnology Inc.

AN959, “Using the PIC16F639 MCU for SmartWireless Applications,” Application Note (DS00950),Microchip Technology Inc.

TB088, “PIC16F639 Microcontroller Overview,”Technical Brief (DS91088) Microchip Technology Inc.

TB090, “MCP2030 Three - Channel Analog Front-EndDevice Overview,” Technical Brief (DS91090A)Microchip Technology Inc.

“MCP2030 Data Sheet”, (DS21981), MicrochipTechnology Inc.

“Coilcraft Data Sheet”, (P/N 4308 and 5315 Series);http://www.coilcraft.com

Base Station Command

TransponderResponse

Step 1

Step 2

Step 3

Step 4


AN1024

APPENDIX A: SOURCE CODEThe complete source code, including any firmwareapplications and necessary support files, is availablefor download as a single archive file from the Microchipcorporate web site, at:

www.microchip.com


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APPENDIX B: TRANSPONDER

FIGURE B-1: TRANSPONDER SCHEMATIC SHEET 1 OF 1


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FIGURE B-2: TOP MASK VIEW OF TRANSPONDER

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FIGURE B-3: BOTTOM MASK VIEW OF TRANSPONDER

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APPENDIX C: BASE STATION

FIGURE C-1: BASE STATION SCHEMATIC SHEET 1 OF 2


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FIGURE C-2: BASE STATION SCHEMATIC SHEET 2 OF 2

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FIGURE C-3: TOP MASK VIEW OF BASE STATION
FIGURE C-4: BOTTOM MASK VIEW OF BASE STATION


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AN1024
NOTES:

Note the following details of the code protection feature on Microchip devices:• Microchip products meet the specification contained in their particular Microchip Data Sheet.

• Microchip believes that its family of products is one of the most secure families 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 knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is 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 ourproducts. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such actsallow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.

Information contained in this publication regarding deviceapplications and the like is provided only for your convenienceand may be superseded by updates. It is your responsibility toensure that your application meets with your specifications.MICROCHIP MAKES NO REPRESENTATIONS ORWARRANTIES OF ANY KIND WHETHER EXPRESS ORIMPLIED, WRITTEN OR ORAL, STATUTORY OROTHERWISE, RELATED TO THE INFORMATION,INCLUDING BUT NOT LIMITED TO ITS CONDITION,QUALITY, PERFORMANCE, MERCHANTABILITY ORFITNESS FOR PURPOSE. Microchip disclaims all liabilityarising from this information and its use. Use of Microchipdevices in life support and/or safety applications is entirely atthe buyer’s risk, and the buyer agrees to defend, indemnify andhold harmless Microchip from any and all damages, claims,suits, or expenses resulting from such use. No licenses areconveyed, implicitly or otherwise, under any Microchipintellectual property rights.

© 2007 Microchip Technology Inc.

Trademarks

The Microchip name and logo, the Microchip logo, Accuron, dsPIC, KEELOQ, KEELOQ logo, microID, MPLAB, PIC, PICmicro, PICSTART, PRO MATE, PowerSmart, rfPIC, and SmartShunt are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

AmpLab, FilterLab, Linear Active Thermistor, Migratable Memory, MXDEV, MXLAB, PS logo, SEEVAL, SmartSensor and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A.

Analog-for-the-Digital Age, Application Maestro, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, ECAN, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, PICkit, PICDEM, PICDEM.net, PICLAB, PICtail, PowerCal, PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, rfPICDEM, Select Mode, Smart Serial, SmartTel, Total Endurance, UNI/O, WiperLock and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

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.

© 2007, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved.

Printed on recycled paper.

DS01024B-page 25

Microchip received ISO/TS-16949:2002 certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona, Gresham, Oregon and Mountain View, California. The Company’s quality system processes and procedures are for its PIC®

MCUs and dsPIC® DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified.


AMERICASCorporate Office2355 West Chandler Blvd.Chandler, AZ 85224-6199Tel: 480-792-7200 Fax: 480-792-7277Technical Support: http://support.microchip.comWeb Address: www.microchip.comAtlantaDuluth, GA Tel: 678-957-9614 Fax: 678-957-1455BostonWestborough, MA Tel: 774-760-0087 Fax: 774-760-0088ChicagoItasca, IL Tel: 630-285-0071 Fax: 630-285-0075DallasAddison, TX Tel: 972-818-7423 Fax: 972-818-2924DetroitFarmington Hills, MI Tel: 248-538-2250Fax: 248-538-2260KokomoKokomo, IN Tel: 765-864-8360Fax: 765-864-8387Los AngelesMission Viejo, CA Tel: 949-462-9523 Fax: 949-462-9608Santa ClaraSanta Clara, CA Tel: 408-961-6444Fax: 408-961-6445TorontoMississauga, Ontario, CanadaTel: 905-673-0699 Fax: 905-673-6509

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