HCS473-SLROM datasheet(27/68 Pages) MICROCHIP

27 / 68 page

 2002 Microchip Technology Inc.

Preliminary

DS40035C-page 25

HCS473

3.2.3.2

PRESENT TRANSPORT CODE

Prior to modifying the device EEPROM, the correct 32-

bit transport code (password) must be presented to

gain write access. This is done with the PRESENT

TRANSPORT CODE command followed by the 32-bit

transport code and CRC calculated on the 3-bit com-

mand and 32 bits of data.

The HCS473 will return an Acknowledge if the trans-

port code matches the value programmed in produc-

tion; write access has been granted.

The next command (usually a write) must begin T

CMD

after the Acknowledge, Figure 3-13.

The present transport code sequence must precede a

write sequence but not necessarily immediately. Per-

haps all four user memory locations will be written and

verified. The present transport code sequence must

precede only the first write to gain write access. The

system may then alternately write and read (verify)

multiple memory locations. Write access remains until

the next time the device returns to Low Power mode -

communication error or T

CMD time out without receiving

another command.

FIGURE 3-13:

PRESENT TRANSPORT CODE SEQUENCE (RF RESPONSE EXAMPLE)

TSF

ACK

CMD

TCODE

CMD

‘0012’

CRC

2 bits

32 bits

Command

CRC

32-Bit

Transport

ACK

Transport ACK

TTPACK

CMD

ADR

DATA

CMD

WRITE Sequence

Address

Command

16-Bit

Write Data

TCMD

Write

Wake Sequence

Previous Command

Response

Inductive In

(LC Pins)

RF Response

(DATA Pin)

TCMD

5 LFTE

TCMD

TFINH

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