HCS412 Datasheet, PDF (2/44 Pages) Microchip Technology – KEELOQ Code Hopping Encoder and Transponder

HCS412
GENERAL DESCRIPTION
The HCS412 combines patented KEELOQ code hop-
ping technology with bi-directional transponder chal-
lenge-and-response security into a single chip solution
for logical and physical access control.
When used as a code hopping encoder, the HCS412 is
ideally suited to keyless entry systems; vehicle and
garage door access in particular. The same HCS412
can also be used as a secure bi-directional transponder
for contactless token verification. These capabilities
make the HCS412 ideal for combined secure access
control and identification applications, dramatically
reducing the cost of hybrid transmitter/transponder
solutions.
1.0 SYSTEM OVERVIEW
Key Terms
The following is a list of key terms used throughout this
data sheet. For additional information on terminology,
please refer to the KEELOQ introductory Technical Brief
(TB003).
• RKE - Remote Keyless Entry.
• PKE - Passive Keyless Entry.
• Button Status - Indicates what transponder but-
ton input(s) activated the transmission. Encom-
passes the 4 button status bits LC0, S2, S1 and
S0 (Figure 3-2).
• Code Hopping - A method by which a code,
viewed externally to the system, appears to
change unpredictably each time it is transmitted
(Section 1.1.3).
• Code word - A block of data that is repeatedly
transmitted upon button activation (Section 3.2).
• Transmission - A data stream consisting of
repeating code words.
• Crypt key - A unique and secret 64-bit number
used to encrypt and decrypt data. In a symmetri-
cal block cipher such as the KEELOQ algorithm,
the encryption and decryption keys are equal and
will therefore be referred to generally as the crypt
key.
• Encoder - A device that generates and encodes
data.
• Encryption Algorithm - A recipe whereby data is
scrambled using a crypt key. The data can only be
interpreted by the respective decryption algorithm
using the same crypt key.
• Decoder - A device that decodes data received
from an encoder.
• Transponder Reader (Reader, for short) - A
device that authenticates a token using bi-direc-
tional communication.
• Decryption algorithm - A recipe whereby data
scrambled by an encryption algorithm can be
unscrambled using the same crypt key.
• Learn – Learning involves the receiver calculating
the transmitter’s appropriate crypt key, decrypting
the received hopping code and storing the serial
number, synchronization counter value and crypt
key in EEPROM (Section 6.1). The KEELOQ prod-
uct family facilitates several learning strategies to
be implemented on the decoder. The following are
examples of what can be done.
- Simple Learning
The receiver uses a fixed crypt key, common
to all components of all systems by the same
manufacturer, to decrypt the received code
word’s encrypted portion.
- Normal Learning
The receiver uses information transmitted
during normal operation to derive the crypt
key and decrypt the received code word’s
encrypted portion.
- Secure Learn
The transmitter is activated through a special
button combination to transmit a stored 60-bit
seed value used to generate the transmitter’s
crypt key. The receiver uses this seed value
to derive the same crypt key and decrypt the
received code word’s encrypted portion.
• Manufacturer’s code - A unique and secret 64-
bit number used to generate unique encoder crypt
keys. Each encoder is programmed with a crypt
key that is a function of the manufacturer’s code.
Each decoder is programmed with the manufac-
turer code itself.
• Anticollision - A scheme whereby transponders
in the same field can be addressed individually
preventing simultaneous response to a command
(Section 4.3.1).
• IFF - Identify Friend or Foe (Section 1.2).
• Proximity Activation - A method whereby an
encoder automatically initiates a transmission in
response to detecting an inductive field
(Section 4.4.1).
• Transport code - An access code, ‘password’
known only by the manufacturer, allowing pro-
gram access to certain secure device memory
areas (Section 4.3.3).
• AGC - Automatic Gain Control.
DS41099C-page 2
Preliminary
© 2002 Microchip Technology Inc.