HCS473 datasheet(30/68 Pages) MICROCHIP

30 / 68 page

HCS473

DS40035C-page 28

Preliminary

 2002 Microchip Technology Inc.

3.2.3.5

WRITE Command

The transponder reader follows the 3-bit WRITE com-

mand with one of eight possible 3-bit address options

indicating which 16-bit EEPROM word to write to

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

mand, address and data bits.

The HCS473 will attempt to write the value into

EEPROM, responding with an Acknowledge sequence

if successful (Figure 3-15).

The following locations are available to write:

• The 64-bit general purpose user EEPROM.

• The 32-bit serial number.

• The16-bit Device Identifiers #1 and #2.

A Transport Code, write access password, protects the

memory locations from undesired modification. The

reader must precede the Write sequence with a suc-

cessful PRESENT TRANSPORT CODE sequence.

Only a correct match with the transport code pro-

grammed during production will allow write access to

the memory locations.

The next command must begin T

CMD after the write

Acknowledge.

The PRESENT TRANSPORT CODE sequence must

precede a WRITE sequence but not necessarily imme-

diately. Perhaps all four user memory locations will be

written and verified. The PRESENT TRANSPORT

CODE sequence must precede only the first write. The

system may then alternately write and read (verify)

multiple

memory

locations.

Write

access

status

remains until the next time the device returns to sleep -

communication error or T

CMD without receiving another

command.

FIGURE 3-16:

WRITE SEQUENCE (RF RESPONSE EXAMPLE)

TCMD

Command

TCMD

Inductive In

(LC Pins)

CMD

ADR

DATA

CMD

‘1012’ 3 bits 16 bits

ACK

CRC

2 bits

WRT

Address

Command

CRC

TFINH

TWRT

Write ACK

16-Bit

Write Data

Optional Next

Command

CMD

TCMD

RF Response

(DATA Pin)

TCMD

LF must remain on if following

with consecutive command

or if waiting for LF response

5 LFTE

Sequence

Previous Command

Sequence

Previous Command

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