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HCS300-ISN Datasheet(PDF) 2 Page - Microchip Technology |
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HCS300-ISN Datasheet(HTML) 2 Page - Microchip Technology |
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2 / 20 page  HCS300 DS21137F-page 2 © 2001 Microchip Technology Inc. The crypt key, serial number and configuration data are stored in an EEPROM array which is not accessible via any external connection. The EEPROM data is pro- grammable but read-protected. The data can be veri- fied only after an automatic erase and programming operation. This protects against attempts to gain access to keys or manipulate synchronization values. The HCS300 provides an easy-to-use serial interface for programming the necessary keys, system parame- ters and configuration data. 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 4-2). • 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 4-1). • 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. The HCS300 code hopping encoder is designed specif- ically for keyless entry systems; primarily vehicles and home garage door openers. The encoder portion of a keyless entry system is integrated into a transmitter, carried by the user and operated to gain access to a vehicle or restricted area. The HCS300 is meant to be a cost-effective yet secure solution to such systems, requiring very few external components (Figure 2-1). Most low-end keyless entry transmitters are given a fixed identification code that is transmitted every time a button is pushed. The number of unique identification codes in a low-end system is usually a relatively small number. These shortcomings provide an opportunity for a sophisticated thief to create a device that ‘grabs’ a transmission and retransmits it later, or a device that quickly ‘scans’ all possible identification codes until the correct one is found. The HCS300 on the other hand, employs the KEELOQ code hopping technology coupled with a transmission length of 66 bits to virtually eliminate the use of code ‘grabbing’ or code ‘scanning’. The high security level of the HCS300 is based on the patented KEELOQ technol- ogy. A block cipher based on a block length of 32 bits and a key length of 64 bits is used. The algorithm obscures the information in such a way that even if the transmission information (before coding) differs by only one bit from that of the previous transmission, the next |
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