HCS512-SLASHP datasheet(6/26 Pages) MICROCHIP

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HCS512

DS40151D-page 6

4.0

DECODER OPERATION

4.1

Learning a Transmitter to a

Receiver

Either the serial number-based learning method or the

seed-based learning method can be selected. The

learning method is selected in the configuration byte. In

order for a transmitter to be used with a decoder, the

transmitter must first be ‘learned’. When a transmitter is

learned to a decoder, the decoder stores the crypt key,

a check value of the serial number and current syn-

chronization value in EEPROM. The decoder must

keep track of these values for every transmitter that is

learned. The maximum number of transmitters that can

be learned is four. The decoder must also contain the

Manufacturer’s Code in order to learn a transmitter.

The Manufacturer’s Code will typically be the same for

all decoders in a system.

The HCS512 has four memory slots. After an “erase

all” procedure, all the memory slots will be cleared.

Erase all is activated by taking LRNIN low for approxi-

mately 10 seconds. When a new transmitter is learned,

the decoder searches for an empty memory slot and

stores the transmitter’s information in that memory slot.

When all memory slots are full, the decoder randomly

overwrites existing transmitters.

4.1.1

LEARNING PROCEDURE

Learning is activated by taking the LRNIN input low for

longer than 64 ms. This input requires an external pull-

up resistor.

To learn a new transmitter to the HCS512 decoder, the

following sequence is required:

Enter Learning mode by pulling LRNIN low for

longer than 64 ms. The LRNOUT output will go

high.

Activate the transmitter until the LRNOUT out-

put goes low indicating reception of a valid code

(hopping message).

Activate the transmitter a second time until the

LRNOUT toggles for 4 seconds (in Secure

Learning mode, the seed transmission must be

transmitted during the second stage of learn by

activating the appropriate buttons on the trans-

mitter).

If LRNIN is taken low momentarily during the

learn status indication, the indication will be ter-

minated. Once a successful learning sequence

is detected, the indication can be terminated

allowing quick learning in a manufacturing

setup.

The transmitter is now learned into the decoder.

Repeat steps 1-4 to learn up to four transmitters.

Learning will be terminated if two non-sequential

codes were received or if two acceptable codes

were not decoded within 30 seconds.

The following checks are performed on the decoder to

determine if the transmission is valid during learn:

• The first code word is checked for bit integrity.

• The second code word is checked for bit integrity.

• The hopping code is decrypted.

• If all the checks pass, the serial number and syn-

chronization counters are stored in EEPROM

memory.

Figure 4-1 shows a flow chart of the learn sequence.

FIGURE 4-1:

LEARN SEQUENCE

Enter Learn

Mode

Wait for Reception

of Second

Compare Discrimination

Value with Serial Number

Use Generated Key

to Decrypt

Equal

Serial number check value

Synchronization counter

Exit

Learn successful. Store:

Learn

Unsuccessful

Yes

Wait for Reception

of a Valid Code

Non-Repeated

Valid Code

Generate Key

from Serial Number

or Seed Value

crypt key

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