HCS301-/P MICROCHIP [Microchip Technology], HCS301-/P Datasheet - Page 9

• Manufacturer Part Number: HCS301-/P
• Description: KEELOQ CODE HOPPING ENCODER
• Manufacturer: MICROCHIP [Microchip Technology]

4.0
4.1
The HCS301 code word is made up of several parts
(Figure 4-1). Each code word contains a 50% duty
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.
FIGURE 4-1:
FIGURE 4-2:
MSb
MSb
2001 Microchip Technology Inc.
Repeat
Repeat
(1 bit)
(1 bit)
TRANSMITTED WORD
Code Word Format
Note: SEED replaces Encrypted Portion when all button inputs are activated at the same time.
(1 bit)
(1 bit)
V
V
50% Duty Cycle
LOW
LOW
Preamble
T
E
CODE WORD FORMAT
CODE WORD ORGANIZATION
34 bits of Fixed Portion
T
Period
S2 S1 S0 S3
P
T
1 1 1 1
Bit
E
Button
Button
Status
Status
T
E
LOGIC ‘0’
LOGIC ‘1’
Header
T
Serial Number
Serial Number
H
(28 bits)
(28 bits)
Encrypted Portion
of Transmission
T
HOP
S2 S1 S0 S3
4.2
The HCS301 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
(Figure 4-2).
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
Button
Status
32 bits of Encrypted Portion
Code Word Organization
Fixed Portion of
Transmission
(2 bits)
OVR
T
(32 bits)
FIX
SEED
(10 bits)
DISC
66 Data bits
Transmitted
LSb first.
Sync Counter
HCS301
Guard
Time
T
(16 bits)
G
DS21143B-page 9
19
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LSb
LSb