HCS473_13 Datasheet, PDF (20/68 Pages) Microchip Technology – KEELOQ® 3-Axis Transcoder

HCS473
The HCS473 anticollision method is that all devices
trained to a given vehicle will have the same 12-bit
vehicle identifier (VID); Most Significant 12 bits of the
device identifier, Table 3-3. The device identifier of up
to 16 transponders trained to access a given vehicle
will differ only in the 4 LSb’s. These 4 bits are referred
to as the token identifier (TID).
TABLE 3-3: DEVICE ID
16-bit Device ID (DEVID)
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
VID
TID
11 10 9 8 7 6 5 4 3 2 1 0 3 2 1 0
The vehicle ID associates the HCS473 with a given
vehicle and the token ID makes it a uniquely address-
able (selectable) 1 of 16 possible devices authorized to
access the vehicle.
Two unique device identifiers are available allowing the
HCS473 to be used with two different vehicles. The
HCS473 responds if the presented VID and TID match
either of the two programmed identifiers.
SELECT TRANSPONDER may still be performed on
devices not configured to require anticollision; commu-
nication can still be isolated to one of multiple devices
in the field. Equally, the same devices will respond to all
command sequences not preceded by the SELECT
TRANSPONDER sequence.
3.2.1.5 Proximity Activation (PXMA)
Enabling the Proximity Activation configuration option
allows the HCS473 to transmit a hopping code trans-
mission in response to detecting an appropriate wake-
up pulse on an LC input pin.
The HCS473 sends a wake-up sequence Acknowl-
edge in response to detecting the LF field (Figure 3-
11). The device then waits TCMD for the LF field’s falling
edge followed by the normal TCMD window waiting for a
transponder command to begin. If no command is
received, a code hopping transmission is generated
and the minimum code words (set with MTX option) are
transmitted. When the transmission completes, the
HCS473 waits a TCMD window for a new command to
begin. If no command is received the device returns to
SLEEP.
Proximity activations are not repeatedly activated when
the device is in the presence of a continuous LF field
(computer monitor, tv,...). The HCS473 must receive an
appropriate wake-up sequence to activate each trans-
mission.
The button status used in the proximity activated code
hopping transmission clears the S0, S1, S2 and S3 but-
ton status flags.
3.2.1.6 Intelligent Damping (DAMP)
A high Q-factor LC antenna circuit connected to the
HCS473 will continue to resonate after a strong LF field
is removed, slowly decaying. The slow decay makes
fast communication near the reader difficult as the
resulting extended high time makes the following low
time disappear.
The Intelligent damping option enables a pulsed, resis-
tive short from the LC pins to LCCOM when the
HCS473 is expecting the incoming LC signal level to go
low. These pulses damp the antenna, dissipating reso-
nant energy for a quicker decay time when the field is
switched off.
The damping pulses are applied between the LCCOM
pin and the individual LC pins, starting 1.2 LFTE from
detecting the bit’s rising edge and repeating until the
LC input goes low. Damp pulse width is 6 s, beginning
every 44 s as shown in Figure 3-9.
Note:
Damping will not reduce the HCS473 inter-
nal LF analog filter discharge time, TFILTF
(Section 3.2.6).
FIGURE 3-9:
INTELLIGENT DAMPING
No Damping
With Damping
Field on
LC pins
LC Output
Signal Level
TDAMP ^{Damping Pulses}
3.2.1.7
Response Options (RFRSP,
LCRSP)
HCS473 responses may optionally be returned on the
DATA pin for long-range RF responses and/or LC pins
for short-range LF responses (Table 3-4). Responses
include both Acknowledge sequences and data
responses.
The options controlling the response path are:
• LC response option (LCRSP)
• RF response option (RFRSP)
If both RF and LF responses are enabled, Acknowl-
edge pulses will occur simultaneously on the DATA and
LC pins; using the LFTE baud rate (Figure 3-11,
Figure 3-19). Data responses will not occur simultane-
ously. The RF response on the DATA pin will occur first
(following the designated Encoder mode format),
immediately followed by the LF response on the LC
pins (Figure 3-20).
DS40035D-page 20
Preliminary
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