hcs512 Microchip Technology Inc., hcs512 Datasheet - Page 13

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

7.3
There are two key generation algorithms implemented in the HCS512 decoder. The
vides a higher level of security than the XOR algorithm. Section 6.1 describes the selection of the algorithms in the con-
figuration byte.
7.3.1
This algorithm uses the K
Key
Key
7.3.2
The two 32-bits seeds are XOR with the manufacturer’s code to form the 64 bit crypt key.
Key
Key
After programming the manufacturer’s code, the HCS512 decoder will automatically activate an Erase All function,
removing all transmitters from the system.
If LRNIN is taken low momentarily during the learn status indication, the indication will be terminated. Once a successful
learning sequence is detected, the indication can be terminated, allowing quick learning in a manufacturing setup.
FIGURE 7-2:
2002 Microchip Technology Inc.
Padding
Upper 32 bits
Lower 32 bits
Upper 32 bits
Lower 32 bits
Padding
Padding
Padding
0000b
0000b
2
6
Key Generation Algorithms
LS 32 bits of Seed Transmission
LS 32 bits of Seed Transmission
K
XOR WITH THE MANUFACTURER’S CODE
EE
MS 28 bits of Seed Transmission
MS 28 bits of Seed Transmission
28-bit Serial Number
28-bit Serial Number
= Decrypt (SourceH)
= Decrypt (SourceL)
= SourceH XOR Manufacturers Code
= SourceL XOR Manufacturers Code
L
Secure Learn XOR (SC_LRN = 1)
OQ
HCS512 KEY GENERATION
Secure Learn (SC_LRN = 1)
Normal Learn (SC_LRN = 0)
DECRYPT ALGORITHM
EE
L
OQ
decryption algorithm and the manufacturer’s code to derive the crypt key as follows:
64 Bit Manufacturers Code
64 Bit Manufacturers Code
Lower 32 bits
Upper 32 bits
Decryption
Decryption
Algorithm
LRN0 = 0
Algorithm
LRN0 = 0
LRN0 = 1
K
K
EE
EE
XOR
L
L
OQ
OQ
MS 32 bits of crypt key
MS 32 bits of crypt key
LS 32 bits of crypt key
LS 32 bits of crypt key
MS 32 bits of crypt key
LS 32 bits of crypt key
K
EE
L
OQ
decryption algorithm pro-
HCS512
DS40151D-page 13