HCS473-SLROM datasheet(23/68 Pages) MICROCHIP

23 / 68 page

 2002 Microchip Technology Inc.

Preliminary

DS40035C-page 21

HCS473

TABLE 3-4:

HCS473 RESPONSE OPTIONS

3.2.1.8

Skip Field Acknowledge (SKIPACK)

The initial Field Acknowledge sequence, occurring dur-

ing the wake-up pulse, may be disabled by enabling the

Skip Field Acknowledge configuration option (SKI-

PACK=1). Omitting the ACK slightly minimizes a

HCS473’s average communication current draw, but

conversely will increase average authentication time as

the wake-up pulse must then be the maximum start-up

filter charge time, T

SFMAX.

3.2.2

TRANSPONDER COMMUNICATION

Data to and from the HCS473 is always sent Least Sig-

nificant bit first. The data length and modulation format

vary with the particular command sequence and the

transmission path.

3.2.2.1

LC Communication Format

Commands from the transponder reader to the

HCS473 as well as the responses from the HCS473

over the low frequency path (LC pins) are Pulse Posi-

tion Modulated (PPM) according to Figure 3-10.

Communication from the transponder reader to a

HCS473 is via the reader amplitude shifting a 125kHz

low frequency (LF) field.

LF responses back to the transponder reader are

achieved by the HCS473 applying a low-resistance

short from the LC pins to LCCOM (configuration option

LCRSP enables LF talkback). This short across the

antenna inputs is detected by the reader as a load on

its 125kHz transmitting antenna.

See Section 5.4 for further details on inductive commu-

nication principles.

FIGURE 3-10:

LC PIN PULSE POSITION

MODULATION (PPM)

3.2.2.2

RF DATA Communication Format

The RF responses on the DATA pin vary with the infor-

mation being returned.

• Acknowledge responses are based on the LF

TE.

• Data code words responses are based on the

TE, using the format determined by the

Encoder mode options, Section 3.1.4.

3.2.2.3

Wake-up Sequence

The transponder reader initiates each communication

sequence by turning on the low frequency field, then

waits for a HCS473 to Acknowledge the field.

The HCS473 enters Transponder Mode after detecting

a signal on any LC low frequency antenna input pin that

has remained high for at least the start-up filter time

SF, Table 7-5. The device then responds with a Field

Acknowledge sequence indicating that it has detected

the LF field, is in Transponder Mode and is ready to

receive commands (Figure 3-11). The wake-up pulse’s

falling edge must then occur within T

CMD of the end of

the Field Acknowledge sequence.

The Field Acknowledge sequence may optionally be

disabled by enabling the Skip Field ACK configuration

option, Section 3.2.1.8.

In both cases, the first command bit must begin within

CMD of the wake-up pulse’s falling edge or the

HCS473 will return to Low Power mode.

RFRSP

LCRSP

Description

No response

Response over the LC pins

Response through the DATA pin

first and then the LC pins

START or

previous bit

1LF

2LF

‘0’

‘1’

1LF

TE 1LFTE

Digital

Representation

125kHz

Digital

Representation

125kHz

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