HCS410-IP Microchip Technology, HCS410-IP Datasheet - Page 25

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

4.3
In a typical decoder operation (Figure 4-4), the key
generation on the decoder side is done by taking the
serial number from a transmission and combining that
with the manufacturer’s code to create the same
encoder key that is stored in the HCS410. Once the
encoder key is obtained, the rest of the transmission
can be decrypted. The decoder waits for a transmission
and immediately checks the serial number to
determine if it is a learned transmitter. If it is, the code
hopping portion of the transmission is decrypted using
the stored key. It uses the discrimination bits to deter-
mine if the decryption was valid. If everything up to this
point is valid, the synchronization counter value
is evaluated.
1997 Microchip Technology Inc.
CH Mode Decoder Operation
Preliminary
FIGURE 4-4:
No
No
No
No
No
Decrypt Transmission
in Temp Location
Serial Number
Save Counter
Transmission
Decryption
Within 32K
Received
Within 16
Counter
Counter
Match
Does
Start
Valid
DECODER OPERATION
TYPICAL CH MODE
Is
Is
?
?
?
?
Is
?
Yes
Yes
Yes
No
Yes
Yes
HCS410
DS40158C-page 25
Command
Execute
Counter
Update
and