HCS500-IP Microchip Technology, HCS500-IP Datasheet - Page 17

• Manufacturer Part Number: HCS500-IP
• Description: KEELOQ CODE HOPPING ENCODER
• 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
activated), along with the synchronization counter value
and some discrimination bits. The non-code hopping
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 number of
FIGURE 7-1:
FIGURE 7-2:
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
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
Repeat
CRC0*
Preamble
ENCODERS
T
Period
P
19
Bit
.
Non-encrypted Data
V
(1 bit)
LOW
LOGIC ‘0’
LOGIC ‘1’
+
Header
Button Status
S2S1S0S3
T
H
Button Status (32 bits)
(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)
HCS500
Guard
Time
T
DS40153B-page 17
G
Counter
16-bit
Sync.
Value
66/67 bits
of Data
Transmitted