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HCS200-SN Datasheet(PDF) 2 Page - Microchip Technology |
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HCS200-SN Datasheet(HTML) 2 Page - Microchip Technology |
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2 / 16 page  HCS200 DS40138A-page 2 Preliminary © 1996 Microchip Technology Inc. The HCS200 operates over a wide voltage range of 3.5 volts to 13.0 volts and has three button inputs in an 8-pin configuration. This allows the system designer the freedom to utilize up to seven functions. The only components required for device operation are the but- tons and RF circuitry, allowing a very low system cost. 1.0 SYSTEM OVERVIEW Key Terms • Manufacturer’s code — a 64-bit word, unique to each manufacturer, used to produce a unique encryption key in each transmitter (encoder). • Encryption Key — a unique 64-bit key generated and programmed into the encoder during the manufacturing process. The encryption key controls the encryption algorithm and is stored in EEPROM on the encoder device. 1.1 Learn The HCS product family facilitates several learn strate- gies to be implemented on the decoder. The following are examples of what can be done. It must be pointed out that their exists some third-party patents on learn- ing strategies and implementation. 1.1.1 NORMAL LEARN The receiver uses the same information that is transmit- ted during normal operation to derive the transmitter’s secret key, decrypt the discrimination value and the synchronization counter. 1.1.2 SECURE LEARN* The transmitter is activated through a special button combination to transmit a stored 48-bit value (random seed) that can be used for key generation or be part of the key. Transmission of the random seed can be dis- abled after learning is completed. The HCS200 is a code hopping encoder device that is designed specifically for keyless entry systems, primarily for vehicles and home garage door openers. It is meant to be a cost-effective, yet secure solution to such systems. The encoder portion of a keyless entry system is meant to be carried by the user and operated to gain access to a vehicle or restricted area. The HCS200 requires very few external components (Figure 2-1). Most low-end keyless entry systems transmit the same code from a transmitter every time a button is pushed. The number of possible code combinations for a low end system is also a relatively small number. These shortcomings provide the means for a sophisticated thief to create a device that ‘grabs’ a transmission and re-transmits it later, or a device that scans all possible combinations until the correct one is found. The HCS200 employs the KEELOQ code hopping encryption algorithm to achieve a high level of security. Code hopping is a method by which the code transmitted from the transmitter to the receiver is different every time a button is pushed. This method, coupled with a transmission length of 66 bits, virtually eliminates the use of code ‘grabbing’ or code ‘scanning’. As indicated in the block diagram on page one, the HCS200 has a small EEPROM array which must be loaded with several parameters before use. The most important of these values are: • A 28-bit serial number which is meant to be unique for every encoder • A 16-bit configuration value • An encryption key that is generated at the time of production • A 16-bit synchronization value The serial number for each transmitter is programmed by the manufacturer at the time of production. The generation of the encryption key is done using a key generation algorithm (Figure 1-1). Typically, inputs to the key generation algorithm are the serial number of the transmitter and a 64-bit manufacturer’s code. The manufacturer’s code is chosen by the system manufacturer and must be carefully controlled. The manufacturer’s code is a pivotal part of the overall system security. FIGURE 1-1: CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION Transmitter Manufacturer’s Serial Number Code Encryption Key Key Generation Algorithm Serial Number Encryption Key Sync Counter . . . HCS200 EEPROM Array * Code Hopping learn patents pending. |
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