HCS410-IP Microchip Technology, HCS410-IP Datasheet - Page 24

• Manufacturer Part Number: HCS410-IP
• Description: KEELOQ CODE HOPPING ENCODER AND TRANSPONDER
• Manufacturer: Microchip Technology

HCS410
4.2
In order for a transmitter to be used with a decoder, the
transmitter must first be ‘learned’. Several learning
strategies can be followed in the decoder implementa-
tion. When a transmitter is learned to a decoder, it is
suggested that the decoder stores the serial number
and current synchronization counter value (synchroni-
zation counter stored in CH Mode only) in EEPROM.
The decoder must keep track of these values for every
transmitter that is learned (Figure 4-2 and Figure 4-3).
FIGURE 4-2:
DS40158C-page 24
Compare Discrimination
Compare Discrimination
Value with Fixed Value
Value with Fixed Value
Synchronization counter
of Second Valid Code
Learn successful Store:
from Serial Number
Use Generated Key
Use Generated Key
Learning an HCS410 to a Receiver
Wait for Reception
Wait for Reception
of a Valid Code
Generate Key
Enter Learn
Serial number
Sequential
Encoder key
to Decrypt
to Decrypt
Counters
Mode
Equal
Equal
Exit
?
?
?
TYPICAL CH MODE LEARN
SEQUENCE
Yes
Yes
Yes
No
No
No
Unsuccessful
Learn
Preliminary
The maximum number of transmitters that can be
learned is only a function of how much EEPROM
memory storage is available. The decoder must also
store the manufacturer’s code in order to learn an
HCS410, although this value will not change in a typical
system so it is usually stored as part of the microcon-
troller ROM code. Storing the manufacturer’s code as
part of the ROM code is also better for security rea-
sons.
FIGURE 4-3:
TYPICAL IFF LEARN
SEQUENCE
Learn successful
Compare Token
and expected
Serial number
Generate Key
Wait for token
Serial Number
to be detected
Encoder key
Perform IFF
From Serial
Enter Learn
Token and
Response
response
with Token
Number
Equal?
Store:
Mode
Exit
Read
1997 Microchip Technology Inc.
Yes
No