HCS512-IP Microchip Technology, HCS512-IP Datasheet - Page 13

• Manufacturer Part Number: HCS512-IP
• Description: KEELOQ CODE HOPPING DECODER
• Manufacturer: Microchip Technology

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 56/66/67 bits
which consists of 32 bits of encrypted data and 24/34/
35 bits of non-encrypted data.
followed 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-
FIGURE 8-1:
FIGURE 8-2:
tion is comprised of the status bits, the function bits,
and the 24/28-bit serial number. The encrypted and
non-encrypted combined sections increase the number
of combinations to 7.38 x 10
1997 Microchip Technology Inc.
*HCS360/361
EE
L
CRC1*
K
Transmission Format (PWM)
OQ
EE
encoder transmission is made up of sev-
L
OQ
CODE WORD TRANSMISSION FORMAT
CODE WORD ORGANIZATION
3/2 bits
Non-encrypted Data
Repeat
CRC0*
Preamble
ENCODERS
T
Period
P
Bit
19
.
(1 bit)
Vlow
Each transmission is
LOGIC ‘0’
LOGIC ‘1’
+
Header
Button Sta-
tus (4 bits)
T
Serial Number and But-
H
ton Status (32 bits)
Encrypted Portion
of Transmission
Serial Number
28-bit
T
HOP
8.2
The HCSXXX encoder transmits a 66/67-bit code word
when a button is pressed. The 66/67-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.
+
Code Word Organization
Encrypted Data
(4 bits)
Button
Status
Fixed Portion of
Transmission
32 bits of Encrypted Data
T
FIX
Discrimina-
(12 bits)
tion bits
HCS512
Guard
Time
Sync Value
T
DS40151C-page 13
G
16-bit
66/67 bits
of Data
Transmitted