hcs512 Microchip Technology Inc., hcs512 Datasheet - Page 12

• Manufacturer Part Number: hcs512
• Description: Keeloq Code Hopping Decoder Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

HCS512
7.0
The HCS512 decoder has two key generation schemes. Normal learning uses the transmitter’s serial number to derive
two input seeds which are 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.
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 crypt key, and SourceL, for the lower 32 bits.
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 60-bit seed encoders:
DS40151D-page 12
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
Manufacturer’s
Number
32 bits
Lower 32 bits
Lower 32 bits
Upper 16 bits
Upper 28 bits
Serial
Seed
Key
Lower 28 bits
+ Serial Number
(with upper 4 bits always zero)
Patched
(with upper 4 bits always zero)
Key Generation
-------------------
Algorithms
Decrypt
Upper 16 bits
XOR
(with upper 4 bits always zero) << 16
Encoder
2002 Microchip Technology Inc.
Key