HCS410-IST MICROCHIP [Microchip Technology], HCS410-IST Datasheet - Page 26

• Manufacturer Part Number: HCS410-IST
• Manufacturer: MICROCHIP [Microchip Technology]

HCS410
4.4
In a typical IFF decoder, the key generation on the
decoder side is done by reading the serial number from
a token and combining that with the manufacturer’s
code to recreate the encoder key that is stored on the
token. The decoder polls for the presence of a token.
Once detected the decoder reads the serial number. If
the token has been learned, the decoder sends a chal-
lenge and reads the token’s response. The decoder
uses the encoder key stored in EEPROM and decrypt
response. The decrypt response is compared to the
challenge. If they match the appropriate output is acti-
vated.
FIGURE 4-8:
DS40158E-page 26
IFF Decoder Operation
EEPROM Array
Serial Number
Manufacturer
IFF Key
Code
BASIC OPERATION OF AN IFF RECEIVER (DECODER)
Information read from HCS410
Serial Number
Algorithm
K
EE
Response
Preliminary
IFF
L
OQ
FIGURE 4-7:
Decrypted
Response
Check for
Match
No
No
No
TYPICAL IFF DECODER
OPERATION
Execute Command
Decrypt response
Send Challenge
 2001 Microchip Technology Inc.
Serial Number
Read Serial
Challenge &
Decrypt the
Detected?
and Read
Response
Response
Number
Match?
Match?
Token
Does
Does
Start
Written to HCS410
Yes
Yes
Yes
Challenge