HCS361 Datasheet, PDF (10/24 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER

HCS361
4.0 TRANSMITTED WORD
4.1 Transmission Format (PWM)
The HCS361 transmission is made up of several parts
(Figure 4-1 and Figure 4-2). Each transmission is
begun with a preamble and a header, followed by the
encrypted and then the fixed data. The actual data is
67 bits which consists of 32 bits of encrypted data and
35 bits of fixed data. Each transmission is followed by
a guard period before another transmission can begin.
Refer to Table and Table for transmission timing spec-
ifications. The encrypted portion provides up to four bil-
lion changing code combinations and includes the
function bits (based on which buttons were activated)
along with the synchronization counter value and dis-
crimination value. The non-encrypted portion is com-
prised of the CRC bits, VLOW bits, the function bits and
the 28/32-bit serial number. The encrypted and non-
encrypted sections combined increase the number of
combinations to 1.47 x 10²⁰.
4.2 Code Word Organization
The HCS361 transmits a 67-bit code word when a but-
ton is pressed. The 67-bit word is constructed from a
Fixed Code portion and an Encrypted Code portion
(Figure 4-3).
The Encrypted Data is generated from 4 function bits,
2 user bits, overflow bit, independent mode bit, and 8
serial number bits, and the 16-bit synchronization value
(Figure 8-4).
The Non-encrypted Code Data is made up of VLOW
bit, 2 CRC bits, 4 function bits, and the 28-bit serial
number. If the extended serial number (32 bits) is
selected, the 4 function code bits will not be transmit-
ted.
FIGURE 4-1: TRANSMISSION FORMAT—VPWM = 0
TRANSMISSION SEQUENCE:
1 CODE WORD
Preamble Sync Encrypt Fixed Guard Preamble Sync Encrypt
CODE WORD:
LOGIC "0"
LOGIC "1"
BIT
TXWAK=1
TBP
TE
BIT
TXWAK=0
TBP
•
Preamble
SPM=1
TXWAK=0
SPM=0
Header
TXWAK=1
Encrypted
Data
Fixed Code
Data
Code Word
Guard
Time
DS40146C-page 10
Preliminary
© 1996 Microchip Technology Inc.