In general, the simplest way to program the flash memory is one flash word at a time (64 bits plus 8 ECC bits if ECC is present). It is possible to program the flash memory with 32-, 16-, or 8-bit (byte) resolution, but special care must be taken when doing so to ensure the following:

1. On devices with ECC, ECC bits must be handled properly to prevent inadvertent ECC errors.
2. The number of program operations applied to a given word line must be monitored to ensure that the maximum word line program limit before erase is not violated.
3. Once a byte has been programmed, the sector containing the byte must be erased before attempting to re-program the same byte.

To program less than one flash word, the CMDBYTEN register must be configured to indicate which bytes in the flash word are to be programmed before starting the program operation. Each bit in CMDBYTEN corresponds to a byte in the flash word to be programmed, including the ECC bits.

Handling ECC

On devices with ECC, programming 64 bits of data at a time ensures that the 8 ECC bits which correspond to the 64-bit data word are also programmed both correctly and at the same time. Doing so prevents ECC errors from occurring if the memory locations are read by the CPU or DMA after programming.

If use of ECC is planned and partial programming is required, one approach is to mask (not program) the ECC bits until all 64 bits of a flash word are programmed, at which time the ECC bits can also be programmed. Programming of ECC bits is masked by clearing BIT8 (0x100) in the CMDBYTEN register. This prevents a situation where the entire sector must be erased each time a program operation is done to re-program ECC bits to match the new 64-bit data. However, in this case, a read to a partially programmed word where the ECC bits are not yet written would result in an ECC error. To avoid an ECC error, the software must either wait until the full 64-bit flash word and the 8 ECC bits are written, or read the data from the uncorrected address space.

Maximum Program Operations per Word Line Before Erase

The device data sheet specifies a maximum limit on the number of program operations per word line before erasure of the sector containing the word line is required. Exceeding this maximum can result in data corruption within the word line.

If 16-bit or greater program operations are performed, and no 16-bit location is programmed more than once before a sector is erased, the maximum limit will never be reached and thus does not need to be considered.

If 8-bit (byte) program operations are performed, the maximum program limit per word line must be considered and not exceeded. Program operations performed on ECC locations, if done independently from other program operations, count towards the number of writes before an erase is required.