HCS412I MICROCHIP [Microchip Technology], HCS412I Datasheet - Page 9

• Manufacturer Part Number: HCS412I
• Description: KEELOQ Code Hopping Encoder and Transponder
• Manufacturer: MICROCHIP [Microchip Technology]

TABLE 3-1:
3.2
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).
FIGURE 3-1:
Note 1: The transmitted button status will reflect the state of the LC0 input when the button inputs are sampled.
(Note 1)
2002 Microchip Technology Inc.
4-Bit Button Status
LC0
X
X
X
X
X
X
X
1
Transmitted Code Word
S2
0
0
0
1
1
1
1
0
S1
50% Duty Cycle
0
1
1
0
0
1
1
0
ENCODER MODE ACTIVATION
CODE WORD FORMAT
Preamble
S0
1
0
1
1
0
0
1
0
T
P
SEED TMPSD
X
X
X
X
X
X
0
0
1
1
0
0
1
1
Header
X
X
X
X
X
X
0
1
0
1
0
1
0
1
T
H
Code hopping transmission
Code hopping transmission
Code hopping transmission
Code hopping code words until time = T
SEED transmissions temporarily enabled until the 7lsb’s of the synchro-
nization counter wrap 7Fh to 00h. Then only code hopping code words.
Code hopping code words until time = T
Code hopping transmission (2 key IFF enabled)
Code hopping transmission
Code hopping transmission
Code hopping transmission
Code hopping transmission
Limited SEED transmissions - temporarily enabled until the 7lsb’s of the
synchronization counter wrap 7Fh to 00h.
SEED transmission
Code hopping transmission (2 key IFF enabled)
Proximity activated code hopping transmission.
Preliminary
Encrypted Portion
of Transmission
T
HOP
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
• If the extended serial number option is enabled
(XSER = 0), the 37 bits include 5 status bits, 4
button status bits and the 28-bit serial number.
(XSER = 1), the 37 bits include 5 status bits and
the 32-bit serial number.
Resulting Transmission
Fixed Portion of
Transmission
T
FIX
DSD
DSD
, then seed code words.
, then seed code words.
HCS412
Guard
Time
T
G
DS41099C-page 9