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HCS200 Datasheet(PDF) 5 Page - Microchip Technology |
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HCS200 Datasheet(HTML) 5 Page - Microchip Technology |
5 / 16 page © 1996 Microchip Technology Inc. Preliminary DS40138A-page 5 HCS200 3.0 EEPROM MEMORY ORGANIZATION The HCS200 contains 192 bits (12 x 16-bit words) of EEPROM memory (Table 3-1). This EEPROM array is used to store the encryption key information, synchronization value, etc. Further descriptions of the memory array is given in the following sections. TABLE 3-1: EEPROM MEMORY MAP 3.1 Key_0 - Key_3 (64-Bit Encryption Key) The 64-bit encryption key is used by the transmitter to create the encrypted message transmitted to the receiver. This key is created and programmed at the time of production using a key generation algorithm. The key generation algorithm may be different from the KEELOQ algorithm. Inputs to the key generation algorithm are the serial number for the particular transmitter being used and the 64-bit manufacturer’s code. While the key generation algorithm supplied from Microchip is the typical method used, a user may elect to create their own method of key generation. This may be done providing that the decoder is programmed with the same means of creating the key for decryption purposes. 3.2 SYNC (Synchronization Counter) This is the 16-bit synchronization value that is used to create the hopping code for transmission. This value will be changed after every transmission. 3.3 Reserved Must be initialized to 0000H. WORD ADDRESS MNEMONIC DESCRIPTION 0 KEY_0 64-bit encryption key (word 0) 1 KEY_1 64-bit encryption key (word 1) 2 KEY_2 64-bit encryption key (word 2) 3 KEY_3 64-bit encryption key (word 3) 4 SYNC 16-bit synchronization value 5 Reserved Set to 0000H 6 SER_0 Device Serial Number (word 0) 7 SER_1 Device Serial Number (word 1) 8 SEED_0 Seed Value (word 0) 9 SEED_1 Seed Value (word 1) 10 Reserved Set to 0000H 11 CONFIG Config Word 3.4 SER_0, SER_1 (Encoder Serial Number) SER_0 and SER_1 are the lower and upper words of the device serial number, respectively. Although there are 32 bits allocated for the serial number, only the lower order 28 bits are transmitted. The serial number is meant to be unique for every transmitter. 3.5 SEED_0, SEED_1 (Seed Word) This is the 2-word (32-bit) seed code that will be transmitted when all three buttons are pressed at the same time. This allows the system designer to implement the secure learn feature or use this fixed code word as part of a different key generation/tracking process. 3.6 Configuration Word The configuration word is a 16-bit word stored in EEPROM array that is used by the device to store information used during the encryption process, as well as the status of option configurations. Further explanations of each of the bits are described in the following sections. TABLE 3-2: CONFIGURATION WORD 3.6.1 DISCRIMINATION VALUE (DISC0 TO DISC11) Bits 14 and 15 should be set to zero. The discrimination value can be programmed with any value to serve as a post decryption check on the decoder end. In a typical system, this will be programmed with the 12 least sig- nificant bits of the serial number or a constant value, which will also be stored by the receiver system after a transmitter has been learned. The discrimination bits are part of the information that form the encrypted por- tion of the transmission. After the receiver has decrypted a transmission, the discrimination bits can be checked against the stored value to verify that the decryption process was valid. Bit Number Bit Description 0 Discrimination Bit 0 1 Discrimination Bit 1 2 Discrimination Bit 2 3 Discrimination Bit 3 4 Discrimination Bit 4 5 Discrimination Bit 5 6 Discrimination Bit 6 7 Discrimination Bit 7 8 Discrimination Bit 8 9 Discrimination Bit 9 10 Discrimination Bit 10 11 Discrimination Bit 11 12 Voltage Trip Point Select (VLOW SEL) 13 Baudrate Select Bit 0 (BSL0) 14 Reserved 15 Reserved |
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