hcs500 Microchip Technology Inc., hcs500 Datasheet - Page 18

• Manufacturer Part Number: hcs500
• Description: Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

HCS500
7.0
7.1
The K
eral parts (Figure 7-1). 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 34/35
bits of non-encrypted data. Each transmission is fol-
lowed by a guard period before another transmission
can begin. The code hopping portion provides up to
four billion changing code combinations and includes
the button status bits (based on which buttons were
activated), along with the synchronization counter
value and some discrimination bits. The non-code hop-
ping portion is comprised of the status bits, the function
FIGURE 7-1:
FIGURE 7-2:
DS40153C-page 18
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
bits, and the 28-bit serial number. The encrypted and
non-encrypted combined sections increase the number
of combinations to 7.38 x 10
7.2
The HCS encoder transmits a 66/69-bit code word
when a button is pressed. The 66/69-bit word is con-
structed from a code hopping portion and a non-code
hopping portion (Figure 7-2).
The Encrypted Data is generated from four button bits,
two overflow counter bits, ten discrimination bits, and
the 16-bit synchronization counter 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
2002 Microchip Technology Inc.
66 Data bits
19
Transmitted
LSb first.
.
T
Sync Counter
E
Guard
Time
(16 bits)
T
T
BP
E
T
E
LSb
LSb