HCS370 HCS370 KEELOQ Code Hopping Encoder FEATURES PACKAGE TYPES PDIP, SOIC, Security TSSOP S0 1 14 VDD Two programmable 32-bit serial numbers S1 2 13 LED Two programmable 64-bit encoder keys S2 3 12 DATA Two programmable 60-bit seed values S3 4 11 Vss Each transmission is unique 67/69-bit transmission code length S4 RFEN 5 10 32-bit hopping code SLEEP/S5 STEP 6 9 Crypt keys are read protected SHIFT VIN 7 8 Operating 2.05-5.5V operation HCS370 BLOCK DIAGRAM Six button inputs Oscillator VIN SLEEP 15 functions available Power Step-up latching regulator STEP and Four selectable baud rates Controller RESET circuit switching Selectable minimum code word completion LED LED driver Battery low signal transmitted to receiver RFEN RF Enable Nonvolatile synchronization data PWM, VPWM, PPM, and Manchester modulation EEPROM Encoder Button queue information transmitted Dual Encoder functionality DATA 32-bit SHIFT register Other VSS Button input port On-chip EEPROM VDD On-chip tuned oscillator (10% over voltage and SHIFT S5 S4 S3 S2 S S 1 0 temperature) Button inputs have internal pull-down resistors LED output GENERAL DESCRIPTION PLL control for ASK and FSK The HCS370 is a code hopping encoder designed for Low external component count secure Remote Keyless Entry (RKE) and secure Step-up voltage regulator remote control systems. The HCS370 utilizes the KEELOQ code hopping technology, which incorpo- Typical Applications rates high security, a small package outline, and low cost to make this device a perfect solution for unidirec- The HCS370 is ideal for Remote Keyless Entry (RKE) tional authentication systems and access control sys- applications. These applications include: tems. Automotive RKE systems The HCS370 combines a hopping code generated by a Automotive alarm systems nonlinear encryption algorithm, a serial number, and Automotive immobilizers status bits to create a secure transmission code. The Gate and garage door openers length of the transmission eliminates the threat of code Identity tokens scanning and code grabbing access techniques. Burglar alarm systems 2002 Microchip Technology Inc. Preliminary DS41111D-page 1HCS370 The crypt key, serial number, and configuration data - Simple Learning are stored in an EEPROM array which is not accessible The receiver uses a fixed crypt key. The crypt via any external connection. The EEPROM data is pro- key is common to every component used by grammable but read protected. The data can be veri- the same manufacturer. fied only after an automatic erase and programming - Normal Learning operation. This protects against attempts to gain The receiver derives a crypt key from the access to keys or manipulate synchronization values. encoder serial number. Every transmitter has In addition, the HCS370 supports a dual encoder. This a unique crypt key. allows two manufacturers to use the same device with- - Secure Learning out having to use the same manufacturers code in The receiver derives a crypt key from the each of the encoders. The HCS370 provides an easy encoder seed value. Every encoder has a to use serial interface for programming the necessary unique seed value that is only transmitted by keys, system parameters, and configuration data. a special button combination. Manufacturers Code A unique and secret 64- 1.0 SYSTEM OVERVIEW bit number used to derive crypt keys. Each encoder is programmed with a crypt key that is a Key Terms function of the manufacturers code. Each The following is a list of key terms used throughout this decoder is programmed with the manufacturer data sheet. For additional information on KEELOQ and code itself. code hopping, refer to Technical Brief (TB003). The HCS370 code hopping encoder is designed specif- RKE - Remote Keyless Entry ically for keyless entry systems. In particular, typical applications include vehicles and home garage door Button Status - Indicates what button input(s) openers. The encoder portion of a keyless entry sys- activated the transmission. Encompasses the 6 tem is integrated into a transmitter carried by the user. button status bits S5, S4, S3, S2, S1 and S0 The transmitter is operated to gain access to a vehicle (Figure 3-2). or restricted area. The HCS370 is meant to be a cost- Code Hopping - A method by which a code, effective yet secure solution to such systems requiring viewed externally to the system, appears to very few external components (Figure 2-1). change unpredictably each time it is transmitted. Most low end keyless entry transmitters are given a Code Word - A block of data that is repeatedly fixed identification code that is transmitted every time a transmitted upon button activation (Figure 3-2). button is pushed. The number of unique identification Transmission - A data stream consisting of codes in a low end system is usually a relatively small repeating code words (Figure 4-1). number. These shortcomings provide an opportunity Crypt Key - A unique and secret 64-bit number for a sophisticated thief to create a device that grabs used to encrypt and decrypt data. In a symmetri- a transmission and retransmits it later or a device that cal block cipher such as the KEELOQ algorithm, quickly scans all possible identification codes until the the encryption and decryption keys are equal and correct one is found. will therefore be referred to generally as the crypt The HCS370, on the other hand, employs the KEELOQ key. code hopping technology coupled with a transmission Encoder - A device that generates and encodes length of 67 bits to virtually eliminate the use of code data. grabbing or code scanning. The high security level of Encryption Algorithm - A recipe whereby data is the HCS370 is based on the patented KEELOQ technol- scrambled using a crypt key. The data can only be ogy. A block cipher based on a block length of 32 bits interpreted by the respective decryption algorithm and a key length of 64 bits is used. The algorithm using the same crypt key. obscures the information in such a way that if a single Decoder - A device that decodes data received hopping code data bit changes (before encryption), sta- from an encoder (i.e., HCS5XX). tistically more than 50% of the encrypted data bits will Decryption Algorithm - A recipe whereby data change. scrambled by an encryption algorithm can be unscrambled using the same crypt key. Learn Learning involves the receiver calculating the transmitters 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. DS41111D-page 2 Preliminary 2002 Microchip Technology Inc.