HCS500-I Datasheet, PDF (15/34 Pages) Microchip Technology – KEELOQ Code Hopping Decoder

HCS500
5.0 DECODER PROGRAMMING
The decoder uses a 2K, 24LC02B serial EEPROM. The memory is divided between system memory that stores the
transmitter information (read protected) and user memory (read/write). Commands to access the user memory are
described in Sections 4.2.5 and 4.2.6.
The following information stored in system memory needs to be programmed before the decoder can be used:
• 64-bit manufacturer’s code
• Decoder configuration byte
Note 1: These memory locations are read protected and can only be written to using the program command with
the device powered up.
2: The contents of the system memory is encrypted by a unique 64-bit key that is stored in the HCS500. To
initialize the system memory, the HCS500’s program command must be used. The EEPROM and HCS500
are matched, and the devices must be kept together. In-circuit programming is therefore recommended.
5.1 Configuration Byte
The decoder is configured during initialization by setting the appropriate bits in the configuration byte. The following table
list the options:
Bit
Mnemonic
Description
0
LRN_MODE Learning mode selection
LRN_MODE = 0—Normal Learn
LRN_MODE = 1—Secure Learn
1
LRN_ALG Algorithm selection
LRN_ALG = 0—KEELOQ Decryption Algorithm
LRN_ALG = 1—XOR Algorithm
2
REPEAT Repeat Transmission enable
0 = Disable
1 = Enabled
3
Not Used Reserved
4
Not Used Reserved
5
Not Used Reserved
6
Not Used Reserved
7
Not Used Reserved
5.1.1 LRN_MODE
LRN_MODE selects between two learning modes. With LRN_MODE = 0, the Normal (serial number derived) mode is
selected; with LRN_MODE=1, the Secure (seed derived) mode is selected. See Section 6.0 for more detail on learning
modes.
5.1.2 LRN_ALG
LRN_ALG selects between the two available algorithms. With LRN_ALG = 0, is selected the KEELOQ decryption
algorithm is selected; with LRN_ALG = 1, the XOR algorithm is selected. See Section 6.0 for more detail on learning
algorithms.
5.1.3 REPEAT
The HCS500 can be configured to indicate repeated transmissions. In a stand-alone configuration, repeated transmis-
sions must be disabled.
© 2002 Microchip Technology Inc.
DS40153C-page 15