2.9 Writing OTP Words

The procedure for writing to user OTP memory is similar to the procedure for writing to user program memory, except that each of the 64 OTP double-word pairs can only be written once. Both words in each OTP location must be written together using the same two-word latch write process used to write code memory.

Writing anything, with the exception of all ‘1’s, to an OTP location generates an ECC checksum and renders that location used. Attempting to write to an OTP location that has already been programmed will cause an ECC checksum error the next time that location is read. Care should be taken to avoid writing to OTP locations that have already been programmed or may need to be programmed at a later time. See Figure 1-7 for the location of user OTP memory.

Figure 2-9 shows a high-level overview of the OTP programming process.