HCS300
4.0
4.1
TRANSMITTED WORD
Code Word Format
4.2
Code Word Organization
The HCS300 code word is made up of several parts
cycle preamble, a header, 32 bits of encrypted data and
34 bits of fixed data followed by a guard period before
another code word can begin. Refer to Table 8-4 for
code word timing.
The HCS300 transmits a 66-bit code word when a
button is pressed. The 66-bit word is constructed from
a Fixed Code portion and an Encrypted Code portion
The 32 bits of
Encrypted Data
are generated from 4
button bits, 12 discrimination bits and the 16-bit sync
value. The encrypted portion alone provides up to four
billion changing code combinations.
The 34 bits of
Fixed Code Data
are made up of 2 sta-
tus bits, 4 button bits and the 28-bit serial number. The
fixed and encrypted sections combined increase the
number of code combinations to 7.38 x 10
19
.
FIGURE 4-1:
CODE WORD FORMAT
T
E
T
E
T
E
LOGIC ‘0’
LOGIC ‘1’
Bit
Period
50% Duty Cycle
Preamble
T
P
Encrypted Portion
of Transmission
T
HOP
Fixed Portion of
Transmission
T
FIX
Guard
Time
T
G
Header
T
H
FIGURE 4-2:
CODE WORD ORGANIZATION
34 bits of Fixed Portion
32 bits of Encrypted Portion
Button
Status
S2 S1 S0 S3
OVR
(2 bits)
DISC
(10 bits)
Sync Counter
(16 bits)
LSb
Repeat V
LOW
(1 bit) (1 bit)
MSb
Button
Status
S2 S1 S0 S3
Serial Number
(28 bits)
66 Data bits
Transmitted
LSb first.
Repeat V
LOW
(1 bit) (1 bit)
Button
Status
1 1 1 1
Serial Number
(28 bits)
SEED
(32 bits)
MSb
LSb
Note:
SEED replaces Encrypted Portion when all button inputs are activated at the same time.
DS21137F-page 8
©
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
