8.3.5 Security Configuration Words

A summary of security related Configuration Words is shown in Table 8-11. Each entry in the table is a 128-bit Flash word that can be independently programmed. Not all 128 bits are used for any Configuration Word; unused bits are reserved. The table shows the primary Configuration Words and their addresses. The Configuration Words have primary and secondary locations, with the secondary location used in case of an uncorrectable bit error when loading the primary location. UCA and UCB secondary word addresses are the primary address + 0x800. FEPUCB and FWPUCB are OTP words that have 32-bit values to prevent inadvertent programming. These words can only be programmed to the specified value (0x84C1F396 for FEPUCB and 0x5B9B12E4 for FWPUCB). If the word has the specified 32-bit value, it is considered programmed and that option is enabled; otherwise, the option is disabled. UCB Configuration Words may not be programmed if any valid bit/field from that Flash word had previously been programmed (not all ones). The UCB overwrite protection is based on the fuse values loaded at Reset, therefore it only takes effect for a word that has been programmed after the next Reset.