HCS515-IP Microchip Technology, HCS515-IP Datasheet - Page 2

• Manufacturer Part Number: HCS515-IP
• Description: KEELOQ CODE HOPPING DECODER
• Manufacturer: Microchip Technology

HCS515
1.0
1.1
• Manufacturer’s Code – A 64-bit word, unique to
• Encoder Decryption Key – A 64-bit key, unique for
• Learn – The receiver uses information that is
The HCS encoders and decoders employ the K
code hopping technology and a K
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’.
FIGURE 1-1:
DS40183A-page 2
each manufacturer, used to produce a unique
encoder decryption key in each transmitter.
each transmitter. The encoder decryption key
controls the K
stored in EEPROM on the decoder device.
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.
K
Key Terms
EE
Manufacturer’s
L
EE
OQ
Code
CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION
L
OQ
SYSTEM OVERVIEW
decryption algorithm and is
Serial Number or
EE
Transmitter
Generation
L
Algorithm
OQ
Seed
Key
encryption
EE
L
Preliminary
OQ
Encryption
1.2
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
• A 16-bit synchronization counter value
• A 28-bit serial number which is meant to be
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.
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 K
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.
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 K
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.
Key
the time of production
unique for every encoder
Note:
HCS Encoder Overview
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.
HCS515 EEPROM Array
EE
L
Encryption Key
Serial Number
OQ
Sync Counter
1998 Microchip Technology Inc.
encryption algorithm, a
.
.
.
Once the encoder
EE
L
OQ