hcs473 Microchip Technology Inc., hcs473 Datasheet - Page 27

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

3.2.3.2
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
after the Acknowledge, Figure 3-13.
FIGURE 3-13:
 2002 Microchip Technology Inc.
Inductive In
RF Response
(LC Pins)
(DATA Pin)
Previous Command
Wake Sequence
Response
or
PRESENT TRANSPORT CODE
T
SF
ACK
PRESENT TRANSPORT CODE SEQUENCE (RF RESPONSE EXAMPLE)
T
CMD
T
CMD
Command
T
CMD
‘001
CMD
2
’
TCODE
Transport
32 bits
32-Bit
CMD
Preliminary
T
TPACK
2 bits
CRC
CRC
Transport ACK
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
another command.
T
5 LF
ACK
FINH
TE
T
T
CMD
CMD
Command
CMD
T
Write
CMD
WRITE Sequence
CMD
ADR
Address
time out without receiving
DATA
HCS473
Write Data
DS40035C-page 25
16-Bit