HCS473 Datasheet, PDF (31/68 Pages) Microchip Technology – Code Hopping Encoder and Transponder

HCS473
3.2.3.6
REQUEST HOPPING CODE
COMMAND
The REQUEST HOPPING CODE command tells the
HCS473 to increment the synchronization counter and
build the 32-bit code hopping portion of the encoder
code word.
A delay of THOP occurs while the HCS473 increments
the counter (updating EEPROM values) and encrypts
the response.
RFRSP determines if the response will be transmitted
on the DATA pin. If enabled, the response will be a sin-
gle KEELOQ code hopping code word, based on
Encoder mode options. The code word will contain a
button code of ‘0000₂’, indicating the transmission did
not result from a button press.
LFRSP determines if the response will be transmitted
on the LC pins. The LC pin response will be the 32-bit
hopping portion of the code word, modulated PPM for-
mat.
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 next command must begin TCMD after the code
hopping response.
FIGURE 3-17:
REQUEST HOPPING CODE SEQUENCE (RF RESPONSE EXAMPLE)
Wake Sequence
or
Previous Command
Response
‘110₂’ 2 bits
TCMD
CMD CRC
Command CRC
THOP
TCMD
RESPONSE
Optional Next
Command
Next
Command
TSF
Inductive In
(LC Pins)
RF Response
(DATA Pin)
TCMD
ACK
TCMD
TFINH
THOP
LF must remain on if following
with consecutive command
or if waiting for LF response
RF Response (RFRSP=1)
TCMD
TCMD
 2002 Microchip Technology Inc.
Preliminary
DS40035C-page 29