HCS412_11 Datasheet, PDF (9/52 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder Burglar alarm systems

HCS412
TABLE 3-1: ENCODER MODE ACTIVATION
4-Bit Button Status
LC0
(Note 1)
S2
S1
S0
SEED TMPSD
Resulting Transmission
X
001
X
X Code hopping transmission
X
010
X
X Code hopping transmission
X
011
0
0 Code hopping transmission
Code hopping code words until time = TDSD, then seed code words.
0
1 SEED transmissions temporarily enabled until the 7lsb’s of the synchro-
nization counter wrap 7Fh to 00h. Then only code hopping code words.
1
0 Code hopping code words until time = TDSD, then seed code words.
1
1 Code hopping transmission (2 key IFF enabled)
X
101
X
X Code hopping transmission
X
100
X
X Code hopping transmission
X
110
X
X Code hopping transmission
X
111
0
0 Code hopping transmission
0
1
Limited SEED transmissions - temporarily enabled until the 7lsb’s of the
synchronization counter wrap 7Fh to 00h.
1
0 SEED transmission
1
1 Code hopping transmission (2 key IFF enabled)
1
000
X
X Proximity activated code hopping transmission.
Note 1: The transmitted button status will reflect the state of the LC0 input when the button inputs are sampled.
3.2 Transmitted Code Word
The HCS412 transmits a 69-bit code word in response
to a button or proximity activation (Figure 3-1). Each
code word contains a 50% duty cycle preamble,
header, 32 bits of encrypted data and 37 bits of fixed
code data followed by a guard period before another
code word can begin.
The 32 bits of Encrypted Data include 4 button bits, 2
counter overflow bits, 10 discrimination bits and the 16-
bit synchronization counter value (Figure 3-2).
The content of the 37 bits of Fixed Code Data varies
with the extended serial number (XSER) option
(Figure 3-2).
• If the extended serial number option is disabled
(XSER = 0), the 37 bits include 5 status bits, 4
button status bits and the 28-bit serial number.
• If the extended serial number option is enabled
(XSER = 1), the 37 bits include 5 status bits and
the 32-bit serial number.
FIGURE 3-1: CODE WORD FORMAT
50% Duty Cycle
Preamble
TP
Header
TH
Encrypted Portion
of Transmission
THOP
Fixed Portion of
Transmission
TFIX
Guard
Time
TG
© 2011 Microchip Technology Inc.
DS41099D-page 9