HCS410_01 Datasheet, PDF (22/36 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder

HCS410
4.0 INTEGRATING THE HCS410
INTO A SYSTEM
Use of the HCS410 in a system requires a compatible
decoder. This decoder is typically a microcontroller with
compatible firmware. Firmware routines that accept
transmissions from the HCS410, decrypt the code hop-
ping portion of the data stream and perform IFF func-
tions are available. These routines provide system
designers the means to develop their own decoding
system.
4.1 Key Generation
The serial number for each transmitter is programmed
by the manufacturer at the time of production. The
generation of the encoder key is done using a key gen-
eration algorithm (Figure 4-1). Typically, inputs to the
key generation algorithm are the serial number of the
transmitter or seed value, and a 64-bit manufacturer’s
code. The manufacturer’s code is chosen by the sys-
tem manufacturer and must be carefully controlled. The
manufacturer’s code is a pivotal part of the overall
system security.
FIGURE 4-1: CREATION AND STORAGE OF ENCODER KEY DURING PRODUCTION
Transmitter
Serial Number or
Seed
Manufacturer’s
Code
Key
Generation
Algorithm
Encoder
Key
HCS410 EEPROM Array
Serial Number
Encoder Key
Sync Counter
.
.
.
DS40158E-page 22
Preliminary
 2001 Microchip Technology Inc.