HCS361_11 Datasheet, PDF (12/42 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder incorporates high security,

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 9-6 and Table 9-6 for transmission tim-
ing specifications. The encrypted portion provides up to
four billion changing code combinations and includes
the function bits (based on which buttons were acti-
vated) along with the synchronization counter value
and discrimination value. The non-encrypted portion is
comprised 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 3-2).
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 9-4).
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:
PWM Transmission Format (MOD = 0)
TRANSMISSION SEQUENCE:
1st CODE WORD
Preamble Header Encrypt Fixed Guard Preamble Header Encrypt
CODE WORD:
Duty Cycle: 1/3-2/3
(TXWAK=0)
Duty Cycle: 1/6-2/6
(TXWAK=1)
LOGIC 0
TE _{LOGIC 1}
TBP=3XTE
LOGIC 0
TBP
TE _{LOGIC 1}
TBP=6XTE
TBP
TXWAK=0 ^TBP
1
6
10
TXWAK=1
33% Duty Cycle
18xTE Preamble
SPM=1
SPM=0
10xTE Sync 10xTE Header Encrypted Portion
Pulse
Code Word
Fixed Code Portion
Guard
Time
DS40146F-page 12
© 2011 Microchip Technology Inc.