APGRD001 Microchip Technology, APGRD001 Datasheet - Page 2

• Manufacturer Part Number: APGRD001
• Description: REF DESIGN PKE PIC16F639
• Manufacturer: Microchip Technology
• Type: PKE, RKEr

Specifications of APGRD001

• Frequency: 125kHz
• Processor To Be Evaluated: PIC16F639
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: PIC16F639, PIC16F636, PIC18F2680
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

AN1024
PIC16F639 PKE TRANSPONDER
The PIC16F639 has a digital MCU section (PIC16F639
core) and an analog front-end (AFE) section. The
device can be used for various low-frequency sensing
and bidirectional smart communication applications.
Figure 1 shows an example of a typical PKE system.
The base station unit transmits a 125 kHz command to
search for a valid transponder in the field. The PKE
transponder sends back a response if the received
command is valid.
The PIC16F639 device has high analog input
sensitivity (up to 1 mV
connection pins. By connecting three antennas that are
positioned to x, y and z directions, the transponder can
pick up signals from any direction at any given time.
Therefore, it reduces the likelihood of missing signals
due to the properties of antenna directionality. The
input signal at each antenna pin is detected
independently and summed afterwards. Each input
channel can be independently enabled or disabled by
programming the Configuration register. The device
consumes less operating power if fewer channels are
enabled.
For hands-free operation, the transponder is continu-
ously waiting and detecting input signals. This presents
an issue for the life expectancy of the battery. There-
fore, in order to reduce the operating current, the digital
MCU section can stay in low-current mode (Sleep),
while the Analog Front-End (AFE) is looking for a valid
input signal. The digital MCU section is waking up only
when the AFE detects a valid input signal. This feature
is possible by using an Output Enable Filter (wake-up
filter). There are nine Output Enable Filter options
available in the PIC16F639. Users can program the
filter using the Configuration register. Once the filter is
programmed, the device passes detected output to the
digital section only if the incoming signal meets the filter
requirement.
Figure 2 shows an example of the PKE transponder
configuration. The transponder consists of the
PIC16F639 device, external LC resonant circuits, push
buttons, a UHF transmitter, battery back-up (optional),
and a 3V lithium battery.
The digital sections have two I/O ports; PORTA and
PORTC. Each of the PORTA pins is individually
configurable as an Interrupt-on-change pin. The pins
on PORTC have no Interrupt-on-change function.
DS01024B-page 2
PP
) and three antenna
The AFE section shares three I/O pins in PORTC of the
digital section; RC1, RC2 and RC3, which are internally
bonded 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 AFE
Configuration registers. Refer to the PIC12F635/
PIC16F636/639 Device Data Sheet (DS41232) for more
details (see “References”).
To save battery power, the digital section is normally in
Sleep mode while the AFE section is detecting LF input
signals. Although the AFE’s output pads are internally
bonded to the PORTC pins, the AFE output cannot
wake-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 the
LFDATA and ALERT pins of the AFE be connected to
the PORTA pins externally, as shown in Figure 2.
The digital section can wake up when one of the
following three conditions occur:
1.
2.
3.
AFE output at LFDATA pin,
AFE output at ALERT pin, or
Any event by push button switches on PORTA.
© 2007 Microchip Technology Inc.