HCS410 datasheet(25/36 Pages) MICROCHIP

25 / 36 page

HCS410

Preliminary

DS40158C-page 25

4.3

CH Mode Decoder Operation

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

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.

FIGURE 4-4:

TYPICAL CH MODE

DECODER OPERATION

Transmission

Received

Does

Serial Number

Match

Decrypt Transmission

Decryption

Valid

Counter

Within 16

Counter

Within 32K

Update

Counter

Execute

Command

Save Counter

in Temp Location

Start

Yes

and

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