HCS360_11 Datasheet, PDF (12/40 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder outline and low cost,

HCS360
4.0 TRANSMITTED WORD
4.1 Transmission Format (PWM)
The HCS360 code word is made up of several parts
(Figure 4-1 and Figure 4-2). Each code word contains
a 50% duty cycle preamble, a header, 32 bits of
encrypted data and 35 bits of fixed data followed by a
guard period before another code word can begin.
Refer to Table 9-3 and Table 9-5 for code word timing.
FIGURE 4-1: CODE WORD FORMAT (PWM)
50% Duty Cycle
Preamble
1
16
4.2 Code Word Organization
The HCS360 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 3-1).
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 3-1). The encrypted portion alone provides up
to four billion changing code combinations.
The Fixed Code Data is made up of a 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 func-
tion code bits will not be transmitted. The fixed and
encrypted sections combined increase the number of
code combinations to 7.38 x 10¹⁹
LOGIC "0"
LOGIC "1"
TE TE TE
31XTE Preamble
10xTE ^{Encrypted Portion}
Header ^{of Transmission}
Fixed Portion
of Transmission
Guard
Time
FIGURE 4-2: CODE WORD FORMAT (MANCHESTER)
12
50% Duty Cycle
Preamble
START bit bit 0 bit 2
bit 1
16
LOGIC "0"
TE TE
LOGIC "1"
STOP bit
31XTE
Preamble
4XTE
Header
Encrypted Portion
of Transmission
Fixed Portion
of Transmission
Guard
Time
DS40152F-page 12
© 2011 Microchip Technology Inc.