HCS473_13 Datasheet, PDF (3/68 Pages) Microchip Technology – KEELOQ® 3-Axis Transcoder

1.0 GENERAL DESCRIPTION
The HCS473 combines the patented KEELOQ code
hopping technology and bi-directional transponder
challenge-and-response security into a single chip
solution for logical and physical access control.
The three-input transponder interface allows the com-
bination of three orthogonal transponder antennas,
eliminating the directionality associated with traditional
single antenna transponder systems.
When used as a code hopping encoder, the HCS473 is
well suited to keyless entry systems; vehicle and
garage door access in particular. The same HCS473
can also be used as a secure bi-directional transponder
for contactless authentication. These capabilities make
the HCS473 ideal for combined secure access control
and identification applications, dramatically reducing
the cost of hybrid transmitter/transponder solutions.
1.1 System Overview
1.1.1 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).
• AGC - Automatic Gain Control.
• Anticollision - A scheme whereby transponders
in the same field can be addressed individually,
preventing simultaneous response to a command
(Section 3.2.1.4).
• Button Status - Indicates what button input(s)
activated the transmission. Encompasses the 4
button status bits S3, 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 1.2.3).
• Code word - A block of data that is repeatedly
transmitted upon button activation (Figure 3-2).
• Crypto 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
crypto key.
• Decoder - A device that decodes data received
from an encoder.
• Decryption algorithm - A recipe whereby data
scrambled by an encryption algorithm can be
unscrambled using the same crypto key.
• Device Identifier - 16-bit value used to uniquely
select one of multiple transponders for communi-
cation.
• Encoder - A device that generates and encodes
data.
HCS473
• Encryption Algorithm - A recipe whereby data is
scrambled using a crypto key. The data can only
be interpreted by the respective decryption algo-
rithm using the same crypto key.
• IFF - Identify Friend or Foe, a classic authentica-
tion method (Section 3.2.3.3).
• Learn - Learning involves the receiver calculating
the transmitter’s appropriate crypto key, decrypt-
ing the received hopping code and storing the
serial number, synchronization counter value and
crypto key in EEPROM (Section 5.1). The
KEELOQ product 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 crypto key, common to
all components of all systems by the same manu-
facturer, to decrypt the received code word’s
encrypted portion.
• Normal Learning
The receiver uses information transmitted during
normal operation to derive the crypto key and
decrypt the received code word’s encrypted por-
tion.
• Secure Learn
The transmitter is activated through a special but-
ton combination to transmit a stored 60-bit seed
value used to derive the transmitter’s crypto key.
The receiver uses this seed value to calculate the
same crypto key and decrypt the received code
word’s encrypted portion.
• LF - Low Frequency. For HCS473 purposes, LF
refers to a typical 125 kHz frequency.
• Manufacturer’s code – A unique and secret 64-
bit number used to generate unique encoder
crypto keys. Each encoder is programmed with a
crypto key that is a function of the manufacturer’s
code. Each decoder is programmed with the man-
ufacturer code itself.
• Proximity Activation - A method whereby an
encoder automatically initiates a transmission in
response to detecting an inductive field
(Section 3.1.1.2).
• PKE - Passive Keyless Entry.
• RKE - Remote Keyless Entry.
• Transmission - A data stream consisting of
repeating code words.
• Transcoder - Device combining unidirectional
transmitter capabilities with bi-directional authenti-
cation capabilities.
• Transponder - A transmitter-receiver activated
for transmission by reception of a predetermined
signal.
 2000-2013 Microchip Technology Inc.
Preliminary
DS40035D-page 3