HCS515-IP Microchip Technology, HCS515-IP Datasheet - Page 17

• Manufacturer Part Number: HCS515-IP
• Description: KEELOQ CODE HOPPING DECODER
• Manufacturer: Microchip Technology

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 66/67 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
bits, and the 28-bit serial number. The encrypted and
non-encrypted combined sections increase the num-
ber of combinations to 7.38 x 10
FIGURE 7-1:
FIGURE 7-2:
1998 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
Repeat
CRC0*
Preamble
ENCODERS
T
Period
P
Bit
Non-encrypted Data
V
(1 bit)
LOW
19
.
LOGIC ‘0’
LOGIC ‘1’
+
Header
Button Status
S2S1S0S3
T
Button Status (32 bits)
H
(4 bits)
Serial Number and
Code Hopping Portion
Preliminary
of Transmission
Number
T
Serial
28-bit
HOP
7.2
The HCS encoder transmits a 66/67-bit code word
when a button is pressed. The 66/67-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
S2S1S0S3
+
Code Word Organization
(4 bits)
Encrypted Data
Fixed Portion of
Transmission
32 bits of Encrypted Data
T
FIX
Discrimination
bits (12 bits)
HCS515
Guard
Time
T
DS40183A-page 17
G
Counter
16-bit
Sync.
Value
66/67 bits
of Data
Transmitted