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HCS515 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - KEELOQ CODE HOPPING DECODER - Microchip Technology

भाग संख्या HCS515
समारोह KEELOQ CODE HOPPING DECODER
मैन्युफैक्चरर्स Microchip Technology 
लोगो Microchip Technology लोगो 
पूर्व दर्शन
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<?=HCS515?> डेटा पत्रक पीडीएफ

HCS515 pdf
HCS515
1.0 KEELOQ SYSTEM OVERVIEW
1.1 Key Terms
• Manufacturer’s Code – A 64-bit word, unique to
each manufacturer, used to produce a unique
encoder decryption key in each transmitter.
• Encoder Decryption Key – A 64-bit key, unique for
each transmitter. The encoder decryption key
controls the KEELOQ decryption algorithm and is
stored in EEPROM on the decoder device.
• Learn – The receiver uses information that is
transmitted to derive the transmitter’s encoder
decryption key, decrypt the discrimination value,
and the synchronization counter in learning mode.
The encoder decryption key is a function of the
manufacturer’s code and the device serial number
and/or seed value.
The HCS encoders and decoders employ the KEELOQ
code hopping technology and a KEELOQ encryption
algorithm to achieve a high level of security. Code
hopping is a method by which the code transmitted
from the transmitter to the receiver is different every
time a button is pushed. This method, coupled with a
transmission length of 66 bits, virtually eliminates the
use of code ‘grabbing’ or code ‘scanning’.
1.2 HCS Encoder Overview
The HCS encoders have a small EEPROM array which
must be loaded with several parameters before use.
The most important of these values are:
• An encoder decryption key that is generated at
the time of production
• A 16-bit synchronization counter value
• A 28-bit serial number which is meant to be
unique for every encoder
The manufacturer programs the serial number for each
encoder at the time of production, while the ‘Key Gen-
eration Algorithm’ generates the encoder decryption
key (Figure 1-1). Inputs to the key generation algorithm
typically consist of the encoder’s serial number and a
64-bit manufacturer’s code, which the manufacturer
creates.
Note:
The manufacturer code is a pivotal part of
the system’s overall security. Conse-
quently, all possible precautions must be
taken and maintained for this code.
The 16-bit synchronization counter is the basis for the
transmitted code changing for each transmission and is
updated each time a button is pressed. Because of the
complexity of the KEELOQ encryption algorithm, a
change in one bit of the synchronization counter value
will result in a large change in the actual transmitted
code. There is a relationship (Figure 1-2) between the
encoder decryption key values in EEPROM and how
they are used in the encoder. Once the encoder
detects that a button has been pressed, the encoder
reads the button and updates the synchronization
counter. The synchronization value is then combined
with the encoder decryption key in the KEELOQ
encryption algorithm, and the output is 32 bits of
encrypted information. This data will change with every
button press, hence, it is referred to as the code hop-
ping portion of the code word. The 32-bit code hopping
portion is combined with the button information and the
serial number to form the code word transmitted to the
receiver.
FIGURE 1-1: CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION
Transmitter
Serial Number or
Seed
Manufacturer’s
Code
Key
Generation
Algorithm
Encryption
Key
HCS515 EEPROM Array
Serial Number
Encryption Key
Sync Counter
.
.
.
DS40183A-page 2
Preliminary
© 1998 Microchip Technology Inc.

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