HCS473-SLROM datasheet(22/68 Pages) MICROCHIP

22 / 68 page

HCS473

DS40035C-page 20

Preliminary

 2002 Microchip Technology Inc.

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

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 T

CMD for the LF field’s falling

edge followed by the normal T

CMD 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 T

CMD 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 LF

TE from

detecting the bit’s rising edge and repeating until the

LC input goes low. Damp pulse width is 6

µs, beginning

every 44

µs as shown in Figure 3-9.

FIGURE 3-9:

INTELLIGENT DAMPING

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 LF

TE baud rate (Figure 3-11,

Figure 3-19). Data responses will not occur simulta-

neously. 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).

16-bit Device ID (DEVID)

9876543210

VID

TID

11 10 9

6 5432103210

Note:

Damping will not reduce the HCS473 inter-

nal LF analog filter discharge time, T

FILTF

(Section 3.2.6).

DAMP

LC Output

Level

Field on

LC pins

No Damping

With Damping

Damping Pulses

Signal

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