HCS473ISLROM datasheet(29/68 Pages) MICROCHIP

29 / 68 page

 2002 Microchip Technology Inc.

Preliminary

DS40035C-page 27

HCS473

3.2.3.4

READ Command

The transponder reader follows the 3-bit READ com-

mand with one of eight possible 3-bit address options

indicating which 16-bit EEPROM word to retrieve

(Table 3-5) and a 2-bit CRC calculated over the com-

mand and address bits.

The HCS473 retrieves the data and returns the 16-bit

response by creating a 32-bit value containing two cop-

ies of the response (Figure 3-15).

RFRSP determines if the response will be transmitted

on the DATA pin. If enabled, the response will follow the

selected Encoder mode code hopping format with the

hopping code replaced with the 32-bit response. The

transmissions will contain a button code of ‘0000’.

LFRSP determines if the response will be transmitted

on the LC pins. The LC pin response will be the 32-bit

result, modulated PPM format.

If both RFRSP and LFRSP are enabled, the HCS473

will send the response on the DATA pin immediately fol-

lowed by the PPM response on the LC pins. Refer to

Section 3.2.1.7 for further response path details.

The following locations are available to read:

• The 64-bit general purpose user EEPROM.

• The 32-bit serial number. The serial number is

also transmitted in each code hopping transmis-

sion.

• The16-bit device identifiers #1 and #2.

The next command must begin T

CMD after the read

response.

FIGURE 3-15:

READ SEQUENCE (RF RESPONSE EXAMPLE)

TSF

ACK

CMD

ADR

CRC

CMD

‘1002’ 3 bits 2 bits

READ

RESPONSE

Address

Command

CRC

TFINH

TREAD

RF Response

Inductive In

RF Response (RFRSP=1)

Wake Sequence

Previous Command

Response

Optional Next

Command

CMD

Command

TCMD

(LC Pins)

(DATA Pin)

TCMD

LF must remain on if following

with consecutive command

or if waiting for LF response

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