HCS473_13 Datasheet, PDF (19/68 Pages) Microchip Technology – KEELOQ® 3-Axis Transcoder

3.2.1 TRANSPONDER OPTIONS
The following HCS473 configuration options influence
the device behavior when in Transponder mode:
• Preamble length select (TPRLS)
• LF Demodulator (LFDEMOD)
• LF Baud rate select (LFBSL)
• Anticollision (ACOL)
• Proximity Activation (PXMA)
• Intelligent Damping (DAMP)
• LC response Enable (LCRSP)
• RF response Enable (RFRSP)
• Skip Field Acknowledge (SKIPACK)
The following sections describe these options in detail.
3.2.1.1
Transponder Preamble Length
Select (TPRLS)
Data responses through the DATA pin use the format
determined by the Encoder mode options, with one
exception/option to shorten the response time. The
response’s preamble can be reduced to 4 high pulses
by setting the transponder preamble length select
option. This only affects the responses as a result of
transponder communication (proximity activation trans-
missions included), not responses resulting from but-
ton input activations. The 4 high pulse short preamble
will be at the same duty cycle defined by the preamble
duty cycle Encoder mode option (PRD).
Note:
The long preamble enable Encoder mode
option (LPRE) holds priority over the tran-
sponder preamble length option.
TABLE 3-2: TRANSPONDER PREAMBLE
LENGTH SELECT (TPRLS)
TPLS LPRE
Description
0
0 Normal - 16 high pulses
X
1 Long - LPRL determines length
1
0 Short - 4 high pulses
3.2.1.2 LF Demodulator (LFDEMOD)
The HCS473 has a LF Demodulator mode useful for
debugging antenna hardware.
Enabling LFDEMOD limits the device to demodulator
only mode. After receiving an appropriate wake-up
sequence, the device enters a loop demodulating the
signal on the LC pins and outputting the resulting digital
representation on the LED pin. The HCS473 remains in
this mode until no edges are detected on the LC pins
for TDEMOD, upon which it will return to Low-power
mode; requiring another wake-up sequence to further
demodulate data.
HCS473
The demodulated signal on the LED pin is accurate to
within +/-10s of the signal on the LC pins. The injected
signal will have baud rate limitations based on the
HCS473’s internal filter charge and discharge times,
Section 3.2.6.
The filter times discussed in Section 3.2.6 will be easily
seen in Demodulator mode. The internal filter delay
may be isolated by communicating to the HCS473
inputting the digital signal into LCX and observing the
signal plus internal filter delays on the LED pin.
LFDEMOD options:
• Disabled - device functions normally
• Enabled - device demodulates signal on LC pins,
outputting digital result on the LED pin.
Note: Damping is disabled when in Demodulator
mode.
3.2.1.3 LF Baud Rate Select (LFBSL)
The LF Baud rate select option allows the user to adjust
the basic pulse width element (LFTE) used for tran-
sponder communication.
LFBSL options:
• 100 s LFTE
• 200 s LFTE
• 400 s LFTE
• 800 s LFTE
All communication to and from the HCS473 through the
LC transponder pins will use the selected LFTE. RF
acknowledges to LF communication, through the DATA
pin, will also use the selected LFTE.
3.2.1.4 Anticollision (ACOL)
Multiple transponders in the same inductive field will
simultaneously respond to inductive commands.
Enabling anticollision prevents multiple HCS473
responses from 'colliding'. Hence the term ‘anticolli-
sion.’
When anticollision (ACOL) is enabled, the first com-
mand received after the device wakes must be either
the SELECT TRANSPONDER or ANTICOLLISION
OFFcommand before the HCS473 will respond to any
other command.
The ANTICOLLISION OFF command may be used to
temporarily bypass anticollision requirements for a sin-
gle communication sequence. It allows communication
with an anticollision enabled HCS473 if the VID and
TID are not known (perhaps during a learning
sequence). See Section 3.2.3.7 for further anticollision
off details.
The SELECT TRANSPONDER command allows the
addressing of and communication to an individual
HCS473, regardless if multiple devices are in the field
(Section 3.2.3.1).
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Preliminary
DS40035D-page 19