HCS515_11 Datasheet, PDF (18/38 Pages) Microchip Technology – KEELOQ® Code Hopping Decoder stand-alone decoder

HCS515
7.0 ENCODERS
7.1 Transmission Format (PWM)
The encoder transmission is made up of several 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 66/69 bits, which
consist of 32 bits of encrypted data and 34/37 bits of
non-encrypted data. Each transmission is followed 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 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 combina-
tions to 7.38 x 10¹⁹.
FIGURE 7-1: TRANSMISSION FORMAT (PWM)
7.2 Code Word Organization
The HCS encoder transmits a 66/69-bit code word
when a button is pressed. The 66/69-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.
LOGIC "0"
LOGIC "1"
TE TE TE
TBP
50% Preamble
10xTE
Header
Encrypted
Portion
Fixed Code
Portion
Guard
Time
FIGURE 7-2:
CODE WORD ORGANIZATION
34 bits of Fixed Portion
32 bits of Encrypted Portion
Repeat VLOW Button
(1-bit) (1-bit) Status
MSb
S2 S1 S0 S3
Serial Number
(28 bits)
Button
OVR DISC Sync Counter
Status (2 bits) (10 bits) (16 bits)
S2 S1 S0 S3
LSb
66 Data bits
Transmitted
LSb first.
Repeat VLOW Button
Serial Number
SEED
(1-bit) (1-bit) Status
(28 bits)
(32 bits)
MSb
1 111
LSb
SEED replaces Encrypted Portion when all button inputs are activated at the same time.
DS40183E-page 18
© 2011 Microchip Technology Inc.