HCS412 Datasheet, PDF (26/44 Pages) Microchip Technology – KEELOQ Code Hopping Encoder and Transponder

HCS412
FIGURE 4-11: IFF CHALLENGE AND RESPONSE
Activate
Field ^ACK
Delay to
Command
Command
Delay to
Delay before
32-bit
Data
32-bit Challenge _{Response Response}
TPU
TATO
TOTD
TIT
01b Preamble
01
ACK
2 LFTE
Start
Communication from reader to HCS412
Communication from HCS412 to reader
Command
2 LFTE
Start
32-bit
Challenge
1 LFTE
Start
32-bit
Response
4.3.7 CODE HOPPING REQUEST
The command tells the HCS412 to increment the syn-
chronization counter and build the 32-bit code hopping
portion of the code word.
• If RF Echo is disabled, the data will be transmitted
on the LC lines only (Figure 4-12).
• If RF Echo is enabled, the data will be transmitted
in a code word on the DATA line followed by the
data transmitted on the LC lines. The DATA line is
transmitted first for passive entry support
(Figure 4-13).
The data format will be the same as described in
Section 3.2.
TABLE 4-8: REQUEST HOPPING CODE COMMANDS
Command
Description
Expected data In
Response
11000 Request Hopping Code transmission
None
32-Bit Hopping Code
FIGURE 4-12: CODE HOPPING REQUEST (RF ECHO DISABLED)
Activate
Field
ACK
Delay to
Command
Command
Delay before
Response
32-bit Response
TPU
TATO
T_OTH
01b Preamble
01
ACK
Communication from reader to HCS412
Communication from HCS412 to reader
2 LFTE
Start
Command
1 LFTE
Start
FIGURE 4-13: CODE HOPPING REQUEST (RF ECHO ENABLED)
Field
ACK
Inductive (LF)
DATA (RF)
LF Communication from reader to HCS412
LF Communication from HCS412 to reader
32-Bit PPM
Response
32-Bit PPM
Response
Field
ACK
DS41099C-page 26
Preliminary
© 2002 Microchip Technology Inc.