HCS473 datasheet(26/68 Pages) MICROCHIP

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HCS473

DS40035C-page 24

Preliminary

 2002 Microchip Technology Inc.

3.2.3.1

SELECT TRANSPONDER

The SELECT TRANSPONDER sequence must imme-

diately follow the HCS473 wake-up. A 12-bit Vehicle ID

(VID) follows the 3-bit command. The 4-bit Token ID

(TID) is sent by pulsing the field to identify which tran-

sponder should respond.

The HCS473 counts each time the field is pulsed (6

TE period), the first pulse setting the counter equal to

0. If the VID matched, the HCS473 will send an

Acknowledge when the TID matches the counter. Any

further TID pulses after the Acknowledge occurs will

deselect the device, putting it back to SLEEP - again

requires a wake-up sequence to communicate.

Any HCS473 that did not match both the presented VID

and TID will return to SLEEP, unselected, remaining

that way until the next wake-up pulse occurs.

The next command must begin T

TSCMD after the

Acknowledge. If the LC input is high a point T

TSCMDMIN

after the Acknowledge ends, the HCS473 will return to

SLEEP, unselected, assuming the transponder reader

is sending additional TID pulse(s) to select a different

device. A device of any TID value may therefore be

uniquely selected, regardless if a device with lower TID

has already acknowledged.

FIGURE 3-12:

TRANSPONDER SELECT SEQUENCE (RF RESPONSE EXAMPLE)

TSF

ACK

CMD

VID

CMD

‘0002’

TID

TTSCMD

12 bits

Command

TID=0

12-Bit

VID

ACK

Transponder Select ACK

1-16

Pulses

CMD

‘XXX’

TID=1

TID=2

TID=3

5 LFTE

6 LFTE

TTSCMD

Command

Example for TID=’0011’

TTSACK

WAKE ACK

Inductive In

(LC Pins)

RF Response

(DATA Pin)

TCMD

16-bit Device Identifier

[ 12-bit Vehicle ID ] [ 4-bit Token ID ]

DID

TID

VID

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