hcs512 Microchip Technology Inc., hcs512 Datasheet - Page 14

• Manufacturer Part Number: hcs512
• Description: Keeloq Code Hopping Decoder Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

HCS512
8.0
8.1
The K
eral parts (Figure 8-1). Each transmission begins with
a preamble and a header, followed by the encrypted
and then the fixed data. The actual data is 66/69 bits
which consists of 32 bits of encrypted data and 34/37
bits of non-encrypted data. Each transmission is fol-
lowed by a guard period before another transmission
can begin. The encrypted portion provides up to four
billion changing code combinations and includes the
button status bits (based on which buttons were acti-
vated) along with the synchronization counter value
and some discrimination bits. The non-encrypted por-
tion is comprised of the status bits, the function bits,
FIGURE 8-1:
FIGURE 8-2:
DS40151D-page 14
MSb
MSb
EE
Repeat
Repeat
(1-bit)
(1-bit)
L
K
Transmission Format (PWM)
OQ
EE
encoder transmission is made up of sev-
L
(1-bit)
(1-bit)
V
V
OQ
SEED replaces Encrypted Portion when all button inputs are activated at the same time.
LOW
LOW
TRANSMISSION FORMAT (PWM)
50%
ENCODERS
CODE WORD ORGANIZATION
34 bits of Fixed Portion
S2 S1 S0 S3
Preamble
1 1 1 1
Button
Button
Status
Status
Serial Number
Serial Number
(28 bits)
(28 bits)
Header
10xT
E
Encrypted
S2 S1 S0 S3
Portion
and the 28-bit serial number. The encrypted and non-
encrypted combined sections increase the number of
combinations to 7.38 x 10
8.2
The HCSXXX encoder transmits a 66/69-bit code word
when a button is pressed. The 66/69-bit word is con-
structed from an encryption portion and a non-
encrypted code portion (Figure 8-2).
The Encrypted Data is generated from four button bits,
two overflow counter bits, ten discrimination bits, and
the 16-bit synchronization value.
The Non-encrypted Data is made up from 2 status
bits, 4 function bits, and the 28/32-bit serial number.
Button
Status
32 bits of Encrypted Portion
Code Word Organization
(2 bits)
LOGIC "0"
OVR
LOGIC "1"
Fixed Code
(32 bits)
SEED
Portion
(10 bits)
DISC
19
2002 Microchip Technology Inc.
.
66 Data bits
Transmitted
LSb first.
T
Sync Counter
E
Guard
Time
(16 bits)
T
T
BP
E
T
E
LSb
LSb