HCS473-SLROM datasheet(32/68 Pages) MICROCHIP

32 / 68 page

HCS473

DS40035C-page 30

Preliminary

 2002 Microchip Technology Inc.

3.2.3.7

ANTI-COLLISION OFF

Anticollision is enabled/disabled for a given device by

the ACOL configuration option. The ANTICOLLISION

OFF command may be used to temporarily bypass

anticollision requirements for a single communication

sequence. It allows communication to an anticollision

enabled HCS473 if the VID and TID are not known

(perhaps during a learning sequence).

The command must immediately follow the wake-up

sequence, Figure 3-18. The HCS473 acknowledges

the command receipt, then reacts to all commands

even if the anticollision (ACOL) configuration option is

enabled and a SELECT TRANSPONDER sequence

has not been performed.

The next command must begin T

CMD after the

Acknowledge.

The HCS473 remains in this anticollision off state until

the next time the device returns to SLEEP - communi-

cation error or T

CMD without receiving another com-

mand. Multiple commands may therefore be sent

without sending the ANTICOLLISION OFF command

prior to each command.

FIGURE 3-18:

ANTICOLLISION OFF SEQUENCE (RF RESPONSE EXAMPLE)

3.2.4

LF RESPONSE CONSIDERATIONS

As LF responses are transmitted by the HCS473 plac-

ing a short across the LC antenna inputs, dissipating

the antenna resonance, the transponder reader must

still be sending the 125 kHz field for LF responses to

work. The low frequency field on-time (T

FINH) must

therefore be approriately adjusted to receive an LF

Acknowledge sequence or LF data response, Figure 3-

19 and Figure 3-20.

3.2.5

CONSECUTIVE COMMAND

CONSIDERATIONS

Transponder commands may consecutively follow one

another to minimize communication time as the wake-

up sequence, device selection, anticollision off and

transport code presentation need not be repeated for

every command.

Consideration must be given to how long the transpon-

der reader keeps the LF signal on after the last data

bit’s rising edge (T

FINH) when a command sequence...

• will be followed by another command sequence

• will result in a LF response

The reason is that the HCS473’s analog LF antenna

input circuitry will return to Low-power mode when the

125 kHz field remains absent; requiring a new wake-up

sequence to continue communication.

The HCS473’s analog section will never return to Low-

power mode during any T

CMD window waiting for an LC

input communication edge, so long as the LF signal

existed up to the beginning of the T

CMD window.

Please refer to Figure 3-19 and Figure 3-20 for exam-

ples on adjusting T

FINH for consecutive commands and

LF responses.

3.2.6

LF COMMUNICATION ANALOG

DELAYS

LF communication edge delays result from the

HCS473’s internal analog circuit as well as the external

LC resonant antennas, Figure 3-21.

The rising and falling edge delays inherent to the

HCS473’s internal filtering are known and specified in

Table 7-5, T

FILTR and TFILTF

The cumulative rising and falling edge delays inherent

to both the series LC transmitting antenna and parallel

LC receiving antennas are design dependent, not a

HCS473 specification.

CMD

CRC

CMD

‘1112’2 bits

CMD

Command

CRC

ACK

TFINH

ACOL Off ACK

TAOACK

WAKE ACK

CMD

‘XXX’

Command

TCMD

Inductive In

(LC Pins)

TSF

ACK

RF Response

(DATA Pin)

TCMD

5 LFTE

TCMD

Command

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