PIC16F639-I/SO Microchip Technology, PIC16F639-I/SO Datasheet - Page 3

• Manufacturer Part Number: PIC16F639-I/SO
• Description: IC MCU FLASH 2KX14 20SOIC
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F639-I/SO

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Peripherals: Brown-out Detect/Reset, LVD, POR, WDT
• Number Of I /o: 11
• Program Memory Size: 3.5KB (2K x 14)
• Program Memory Type: FLASH
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 3.6 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 20-SOIC (7.5mm Width)
• For Use With: AC162066 - HEADER INTRFC MPLAB ICD2 20PINAC164039 - MODULE SKT PROMATE II 20DIP/SOIC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Data Converters: -
• Connectivity: -

LF Signal Detection and Detector Output
To detect the LF signal, or to send a response with LF,
the device needs external LC parallel resonant circuits
at the LF input pins. The LC resonant antenna
becomes most sensitive when the antenna is tuned
precisely to the frequency of interest (carrier frequency
of the base station). Each LF input channel has dynam-
ical programmable tuning capacitance up to 63 pF
(1 pF per step) to compensate for the discrepancy in
frequency tuning due to the variation of external
component tolerance of the LC resonant circuits.
The analog front-end functions are controlled by its
eight Configuration registers, which can be dynamically
reprogrammed by the microcontroller firmware based
on real-time signal conditions and applications. The
analog front-end outputs demodulated data, a carrier
clock or a received signal strength indicator (RSSI
current) by controlling the output selection bit of the
internal Configuration register.
When the RSSI output is selected, the device outputs
analog current proportional to the input signal strength.
The RSSI feature can be effectively used for tuning the
LC resonant antenna and distance measurement from
the signal source. The digitized value of the RSSI can
be obtained by implementing a firmware-based ADC.
The digitized value of the RSSI output can be transmit-
ted to the base station for further information. For
example, on the LC resonant antenna tuning, the
device selects its internal resonant capacitor while
monitoring the RSSI value until the highest RSSI value
is found. This antenna tuning can be accomplished by
firmware, which saves the system manufacturer’s labor
intense time for the manual LC tuning during the
assembly process.
The device can be configured to detect amplitude-
modulated input signals with various modulation depths
(8%, 14%, 33% and 60%). For example, if the device is
configured to 8% minimum modulation depth, it can
demodulate the input signal in a noisy environment more
efficiently than with a higher modulation depth setting. In
addition, it can also detect the signal when it is very close
to the base station antenna, where the modulation depth
of the amplitude-modulated signal becomes weaker due
to a long decay time of strong RF signals.
A significant advantage that the PIC16F639 device
has, when compared to similar devices in the market-
place, is that it can demodulate weakly modulated input
signals.
Figure 2 shows an example of the device’s demodulated
output for an input signal with 2 mV
about 14% modulation depth. In this example, the
device’s minimum modulation depth setting is 8% and
the output enable filter (wake-up filter) is enabled.
The output appears right after the output enable filter’s
waveform. For more information on the output enable
filter and minimum modulation depth settings, see the
“ PIC12F635/PIC16F636/639 Data Sheet ” (DS41232).
© 2005 Microchip Technology Inc.
PP
amplitude and
When the device detects valid input signals, it sends a
message to the base station via an external UHF trans-
mitter or the internal LF talk-back modulator of each
channel. The K
eral of the microcontroller allows it to transmit and
receive encrypted data for secure data communica-
tions.
The dynamically reconfigurable output enable (wake-up)
filter allows the microcontroller to wake-up only after a
predefined signal has been received, thus keeping
current consumption to a minimum, but ignoring all other
unwanted signals. The output enable (wake-up) filter
consists of high and low durations of the pulse in the
header of the input data stream. The user has the choice
of up to 8 different output enable (wake-up) filter
settings.
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DS91088B-page 3