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HCS512 Datasheet(PDF) 2 Page - Microchip Technology |
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HCS512 Datasheet(HTML) 2 Page - Microchip Technology |
2 / 26 page HCS512 DS40151D-page 2 © 2002 Microchip Technology Inc. The HCS512 operates over a wide voltage range of 3.0 volts to 6.0 volts. The decoder employs automatic baud rate detection which allows it to compensate for wide variations in transmitter data rate. The decoder contains sophisticated error checking algorithms to ensure only valid codes are accepted. 1.0 SYSTEM OVERVIEW Key Terms The following is a list of key terms used throughout this data sheet. For additional information on KEELOQ and Code Hopping, refer to Technical Brief 3 (TB003). • RKE - Remote Keyless Entry • Button Status - Indicates what button input(s) activated the transmission. Encompasses the 4 button status bits S3, S2, S1 and S0 (Figure 8-2). • Code Hopping - A method by which a code, viewed externally to the system, appears to change unpredictably each time it is transmitted. • Code word - A block of data that is repeatedly transmitted upon button activation (Figure 8-1). • Transmission - A data stream consisting of repeating code words (Figure 8-1). • 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. • 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. The KEELOQ product family facil- itates several learning strategies to be imple- mented 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. 1.1 HCS Encoder Overview The HCS encoders have a small EEPROM array which must be loaded with several parameters before use. The most important of these values are: • A crypt key that is generated at the time of pro- duction • A 16-bit synchronization counter value • A 28-bit serial number which is meant to be unique for every encoder The manufacturer programs the serial number for each encoder at the time of production, while the ‘Key Gen- eration Algorithm’ generates the crypt key (Figure 1-1). Inputs to the key generation algorithm typically consist of the encoder’s serial number and a 64-bit manufac- turer’s code, which the manufacturer creates. Note: The manufacturer code is a pivotal part of the system’s overall security. Conse- quently, all possible precautions must be taken and maintained for this code. |
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