HCS200 HCS200 KEELOQ Code Hopping Encoder FEATURES DESCRIPTION The HCS200 from Microchip Technology Inc. is a code Security hopping encoder designed primarily for Remote Key- Programmable 28-bit serial number less Entry (RKE) systems. The device utilizes the KEELOQ code hopping technology, incorporating high Programmable 64-bit crypt key security, a small package outline and low cost. The Each transmission is unique HCS200 is a perfect replacement of fixed code devices 66-bit transmission code length in unidirectional remote keyless entry systems and 32-bit hopping code access control systems. 28-bit serial number, 4-bit button status, low battery indicator transmitted PACKAGE TYPES Crypt keys are read protected PDIP, SOIC Operating 8 S0 VDD 1 3.513.0V operation 7 NC 2 Three button inputs - seven functions available S1 Selectable baud rate 6 PWM 3 S2 Automatic code word completion VSS NC Low battery signal transmitted to receiver 4 5 Non-volatile synchronization data BLOCK DIAGRAM Other Easy to use programming interface Oscillator Power latching and On-chip EEPROM Controller RESET circuit switching On-chip oscillator and timing components Button inputs have internal pull-down resistors Low external component cost EEPROM Encoder Typical Applications The HCS200 is ideal for Remote Keyless Entry (RKE) PWM 32-bit shift register applications. These applications include: Fixed code replacement Vss Automotive RKE systems Button input port VDD Automotive alarm systems Automotive immobilizers S2 S1 S0 Gate and garage door openers Identity tokens The HCS200 operates over a wide voltage range of 3.5 volts to 13.0 volts and has three button inputs in an Burglar alarm systems 8-pin configuration. This allows the system designer the freedom to implement up to seven functions. The only components required for device operation are the buttons and RF circuitry, allowing a very low systemcost. 2002 Microchip Technology Inc. DS40138C-page 1HCS200 The HCS200 combines a 32-bit hopping code, Learn Learning involves the receiver calculating generated by a non-linear encryption algorithm, with a the transmitters appropriate crypt key, decrypting 28-bit serial number and 6 information bits to create a the received hopping code and storing the serial 66-bit code word. The code word length eliminates the number, synchronization counter value and crypt threat of code scanning and the code hopping mecha- key in EEPROM. The KEELOQ product family facil- nism makes each transmission unique, thus rendering itates several learning strategies to be imple- code capture and resend schemes useless. mented on the decoder. The following are examples of what can be done. The crypt key, serial number and configuration data are - Simple Learning stored in an EEPROM array which is not accessible via The receiver uses a fixed crypt key, common any external connection. The EEPROM data is pro- to all components of all systems by the same grammable but read-protected. The data can be veri- manufacturer, to decrypt the received code fied only after an automatic erase and programming words encrypted portion. operation. This protects against attempts to gain access to keys or manipulate synchronization values. - Normal Learning The HCS200 provides an easy to use serial interface The receiver uses information transmitted for programming the necessary keys, system parame- during normal operation to derive the crypt ters and configuration data. key and decrypt the received code words encrypted portion. - Secure Learn 1.0 SYSTEM OVERVIEW The transmitter is activated through a special Key Terms button combination to transmit a stored 60-bit seed value used to generate the transmitters The following is a list of key terms used throughout this crypt key. The receiver uses this seed value data sheet. For additional information on KEELOQ and to derive the same crypt key and decrypt the Code Hopping, refer to Technical Brief 3 (TB003). received code words encrypted portion. RKE - Remote Keyless Entry Manufacturers code A unique and secret 64- Button Status - Indicates what button input(s) bit number used to generate unique encoder crypt activated the transmission. Encompasses the 4 keys. Each encoder is programmed with a crypt button status bits S3, S2, S1 and S0 (Figure 4-2). key that is a function of the manufacturers code. Code Hopping - A method by which a code, Each decoder is programmed with the manufac- viewed externally to the system, appears to turer code itself. change unpredictably each time it is transmitted. The HCS200 code hopping encoder is designed specif- Code word - A block of data that is repeatedly ically for keyless entry systems primarily vehicles and transmitted upon button activation (Figure 4-1). home garage door openers. The encoder portion of a Transmission - A data stream consisting of keyless entry system is integrated into a transmitter, repeating code words (Figure 8-2). carried by the user and operated to gain access to a Crypt key - A unique and secret 64-bit number vehicle or restricted area. The HCS200 is meant to be used to encrypt and decrypt data. In a symmetri- a cost-effective yet secure solution to such systems, cal block cipher such as the KEELOQ algorithm, requiring very few external components (Figure 2-1). the encryption and decryption keys are equal and Most low-end keyless entry transmitters are given a will therefore be referred to generally as the crypt fixed identification code that is transmitted every time a key. button is pushed. The number of unique identification Encoder - A device that generates and encodes codes in a low-end system is usually a relatively small data. number. These shortcomings provide an opportunity Encryption Algorithm - A recipe whereby data is for a sophisticated thief to create a device that grabs scrambled using a crypt key. The data can only be a transmission and retransmits it later, or a device that interpreted by the respective decryption algorithm quickly scans all possible identification codes until the using the same crypt key. correct one is found. Decoder - A device that decodes data received The HCS200, on the other hand, employs the KEELOQ from an encoder. code hopping technology coupled with a transmission Decryption algorithm - A recipe whereby data length of 66 bits to virtually eliminate the use of code scrambled by an encryption algorithm can be grabbing or code scanning. The high security level of unscrambled using the same crypt key. the HCS200 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 DS40138C-page 2 2002 Microchip Technology Inc.