HCS500T-ISLASHST datasheet(5/42 Pages) MICROCHIP

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DS40000153E-page 5

HCS500

3.0

DECODER OPERATION

3.1

Learning a Transmitter to a

Receiver (Normal or Secure Learn)

Before the transmitter and receiver can work together,

the receiver must first ‘learn’ and store the following

information from the transmitter in EEPROM:

• A check value of the serial number

• The crypt key

• The current synchronization counter value

The decoder must also store the manufacturer’s code

(Section 1.1 “HCS Encoder Overview”) in protected

memory. This code will typically be the same for all of

the decoders in a system.

The

HCS500

has

seven

memory

slots,

and,

consequently, can store up to seven transmitters.

During the learn procedure, the decoder searches for

an empty memory slot for storing the transmitter’s

information. When all of the memory slots are full, the

decoder will overwrite the last transmitter’s information.

To erase all of the memory slots at once, use the

ERASE_ALL command (C3H).

3.2

Learning Procedure

Learning is initiated by sending the ACTIVATE_LEARN

(D2H) command

to the

decoder.

The decoder

acknowledges reception of the command by pulling the

data line high.

For the HCS500 decoder to learn a new transmitter, the

following sequence is required:

Activate the transmitter once.

Activate the transmitter a second time. (In

Secure Learning mode, the seed transmission

must be transmitted during the second stage of

learn by activating the appropriate buttons on

the transmitter.)

The HCS500 will transmit a learn-status string,

indicating that the learn was successful.

The decoder has now learned the transmitter.

Repeat steps 1-3 to learn up to seven

transmitters

Note 1: Learning

will

terminated

two

nonsequential codes were received or if

two acceptable codes were not decoded

within 30 seconds.

2: If

than

seven

transmitters

are

learned, the new transmitter will replace

the last transmitter learned. It is, therefore,

not possible to erase lost transmitters by

repeatedly learning new transmitters. To

remove

lost

stolen

transmitters,

ERASE_ALL transmitters and relearn all

available transmitters.

3: Learning a transmitter with a crypt key that

is identical to a transmitter already in mem-

ory replaces the existing transmitter. In

practice, this means that all transmitters

should have unique crypt keys. Learning a

previously learned transmitter does not use

any additional memory slots.

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