hcs473 Microchip Technology Inc., hcs473 Datasheet - Page 30

• Manufacturer Part Number: hcs473
• Description: Code Hopping Encoder And Transponder
• Manufacturer: Microchip Technology Inc.

HCS473
3.2.3.5
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-
FIGURE 3-16:
DS40035C-page 28
RF Response
Inductive In
(LC Pins)
(DATA Pin)
Previous Command
Previous Command
Sequence
Sequence
WRITE Command
WRITE SEQUENCE (RF RESPONSE EXAMPLE)
T
CMD
T
CMD
Command
‘101
CMD
T
CMD
2
’ 3 bits 16 bits
ADR
Address
DATA
Preliminary
Write Data
16-Bit
2 bits
CRC
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
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
command.
CRC
T
WRT
T
FINH
LF must remain on if following
or if waiting for LF response
T
with consecutive command
WRT
ACK
 2002 Microchip Technology Inc.
CMD
Write ACK
5 LF
without receiving another
TE
T
CMD
CMD
T
CMD
after the write
Command
Optional Next
Command
Next
T
CMD