HCS512-ISN MICROCHIP [Microchip Technology], HCS512-ISN Datasheet - Page 11

• Manufacturer Part Number: HCS512-ISN
• Description: KEELOQ CODE HOPPING DECODER
• Manufacturer: MICROCHIP [Microchip Technology]

7.0
The HCS512 decoder has two key generation schemes. Normal learning uses the transmitter’s serial number to derive
FIGURE 7-1:
7.1
The two input seeds are composed from the serial number in two ways, depending on the encoder type. The encoder
type is determined from the number of bits in the incoming transmission. SourceH is used to calculate the upper 32 bits
of the encoder key, and SourceL, for the lower 32 bits.
For 24-bit serial number encoders (56-bit transmissions):
For 28-bit serial number encoders (66 / 67-bit transmissions):
7.2
The two input seeds are composed from the seed value that is transmitted during secure learning. The lower 32 bits of
the seed transmission is used to compose the lower seed, and the upper 32 bits, for the upper seed. The upper 4 bits
(function code) are set to zero.
For 32-bit seed encoders:
For 48-bit seed encoders:
For 64-bit seed encoders:
two input seeds which a re used as inputs to the key generation algorithm. Secure learning uses the seed transmission
to derive the two input seeds. Two key generation algorithms are available to convert the inputs seeds to secret keys.
The appropriate scheme is selected in the configuration word.
1997 Microchip Technology Inc.
Note:
SourceH = 65H + 24 bit Serial Number
SourceL = 2BH + 24 bit Serial Number
SourceH = 6H + 28 bit Serial Number
SourceL = 2H + 28 bit Serial Number
SourceH = Serial Number
SourceL = Seed
SourceH = Seed
SourceL = Seed
SourceH = Seed
SourceL = Seed
Normal Learning (Serial Number Derived)
Secure Learning (Seed Derived)
KEY GENERATION SCHEMES
64-bit seeds are handled as 48-bit seeds
Manufacturer’s
Number
32 bits
Lower 32 bits
Lower 32 bits
Upper 16 bits
Upper 16 bits
Serial
Seed
Key
Lower 28 bits
+ Serial Number
+ Serial Number
Patched
with upper 4 bits always zero
Key Generation
-------------------
Algorithms
Decrypt
Upper 16 bits
Upper 16 bits
XOR
with upper 4 bits always zero
with upper 4 bits always zero
Encoder
Key
HCS512
DS40151C-page 11