HCS412I MICROCHIP [Microchip Technology], HCS412I Datasheet - Page 25

• Manufacturer Part Number: HCS412I
• Description: KEELOQ Code Hopping Encoder and Transponder
• Manufacturer: MICROCHIP [Microchip Technology]

FIGURE 4-9:
FIGURE 4-10: PROGRAMMING - VERIFICATION
4.3.6
The transponder reader sends one of four possible IFF
commands indicating which crypt key and which algo-
rithm to use to encrypt the challenge (Table 4-7).
The command is followed by the 32-bit challenge, typi-
cally a random number. The HCS412 encrypts the
challenge using the designated crypt key and algorithm
and responds with the 32-bit encrypted result. The
reader authenticates the response by comparing it to
the expected value.
TABLE 4-7:
Command
2002 Microchip Technology Inc.
10000
10001
10100
10101
Communication from reader to HCS412
Communication from HCS412 to reader
Communication from reader to HCS412
Communication from HCS412 to reader
IFF CHALLENGE AND RESPONSE
IFF using key-1 and IFF algorithm
IFF using key-1 and HOP algorithm
IFF using key-2 and IFF algorithm
IFF using key-2 and HOP algorithm
PROGRAM SEQUENCE - CONSECUTIVE WORDS
CHALLENGE AND RESPONSE COMMANDS
1 LF
Start
TE
Description
0 1
Write 18x16-bit
01b Preamble
words total.
Approximately 1ms
Response
delay before verify
begins.
16-bit
Preliminary
Expected data In
32-Bit Challenge
32-Bit Challenge
32-Bit Challenge
32-Bit Challenge
The second crypt key and the seed value occupy the
same EEPROM storage area. To use the second crypt
key for IFF, the Seed Enable (SEED) and the Tempo-
rary Seed Enable (TMPSD) configuration options must
be disabled.
Write 18x16-bit
Note: If seed transmissions are not appropriately
words total.
3LF
each 16-bit word
disabled, the HCS412 will default to using
KEY1 for IFF.
TE
Verify 18x16-bit
words total.
Delay between
32-Bit Response
32-Bit Response
32-Bit Response
32-Bit Response
Response
HCS412
DS41099C-page 25
Start
Verify