HCS360_01 Datasheet, PDF (3/28 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder

HCS360
Any type of controller may be used as a receiver, but it
is typically a microcontroller with compatible firmware
that allows the receiver to operate in conjunction with a
transmitter, based on the HCS360. Section 7.0
provides more detail on integrating the HCS360 into a
total system.
Before a transmitter can be used with a particular
receiver, the transmitter must be ‘learned’ by the
receiver. Upon learning a transmitter, information is
stored by the receiver so that it may track the
transmitter, including the serial number of the
transmitter, the current synchronization value for that
transmitter and the same encryption key that is used on
the transmitter. If a receiver receives a message of
valid format, the serial number is checked and, if it is
from a learned transmitter, the message is decrypted
and the decrypted synchronization counter is checked
against what is stored. If the synchronization value is
verified, then the button status is checked to see what
operation is needed. Figure 1-3 shows the relationship
between some of the values stored by the receiver and
the values received from the transmitter.
FIGURE 1-1: CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION
Transmitter
Serial Number or
Seed
Manufacturer’s
Code
Key
Generation
Algorithm
Encryption
Key
HCS360 EEPROM Array
Serial Number
Encryption Key
Sync Counter
.
.
.
FIGURE 1-2: BASIC OPERATION OF TRANSMITTER (ENCODER)
Transmitted Information
EEPROM Array
Decryption Key
Sync Counter
Serial Number
KEELOQ
Encryption
Algorithm
32 Bits of
Encrypted Data
Serial Number
Button Press
Information
FIGURE 1-3: BASIC OPERATION OF RECEIVER (DECODER)
EEPROM Array
Decryption Key
Sync Counter
Serial Number
Manufacturer Code
Check for
Match
KEELOQ
Decryption
Algorithm
Check for
Match
Decrypted
Synchronization
Counter
Button Press
Information
Serial Number
32 Bits of
Encrypted Data
Received Information
 2001 Microchip Technology Inc.
DS40152D-page 3