hcs515 Microchip Technology Inc., hcs515 Datasheet - Page 5

• Manufacturer Part Number: hcs515
• Description: Keeloq Code Hopping Decoder Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

3.0
3.1
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 encoder decryption key
• The current synchronization counter value
The decoder must also store the manufacturer’s code
(Section 1.1) in protected memory. This code will
typically be the same for all of the decoders in a sys-
tem.
The HCS515 has seven memory slots, and, conse-
quently, 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
command (C3H).
3.1.1
Learning
ACTIVATE_LEARN
The decoder acknowledges reception of the command
by pulling the data line high.
For the HCS515 decoder to learn a new transmitter, the
following sequence is required:
1.
2.
3.
4.
5.
Note 1: Learning will be terminated if two
2002 Microchip Technology Inc.
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 HCS515 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
2: If more than seven transmitters are
DECODER OPERATION
Learning a Transmitter to a
Receiver (Normal or Secure Learn)
nonsequential codes were received or
if two acceptable codes were not
decoded within 30 seconds.
LEARNING PROCEDURE
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 or
stolen
transmitters and relearn all available
transmitters.
is
initiated
transmitters,
(D2H) command to the decoder.
by
ERASE_ALL
sending
ERASE_ALL
the
The following checks are performed by 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 encoder decryption key is generated accord-
• The hopping code is decrypted.
• The discrimination value is checked.
• If all the checks pass, the key, serial number
Figure 3-1 shows a flow chart of the learn sequence.
FIGURE 3-1:
ing to the selected algorithm.
check value, and synchronization counter values
are stored in EEPROM memory.
Serial Number Check Value
Value with Serial Number
Compare Discrimination
Learn Successful Store:
Encoder Decryption Key
from Serial Number/
Sync. Counter Value
Use Generated Key
Wait for Reception
3: Learning a transmitter with an encoder
Wait for Reception
Non-Repeated
of a Valid Code
Generate Key
decryption key that is identical to a
transmitter
replaces the existing transmitter. In
practice, this means that all transmit-
ters should have unique encoder
decryption keys. Learning a previously
learned transmitter does not use any
additional memory slots.
Enter Learn
Seed Value
of Second
Valid Code
to Decrypt
Mode
Equal?
Exit
LEARN SEQUENCE
Yes
already
No
HCS515
Unsuccessful
in
DS40183D-page 5
Learn
memory