30.6.4.3 FLASH, DATA FLASH Write

Data to be written to the NVM block are first written to and stored in an internal buffer called the page buffer. The page buffer contains the same number of bytes as an NVM page. Writes to the page buffer must be 16 or 32 bits. 8-bit writes to the page buffer are not allowed and will cause a bus error.

Both FLASH and Data FLASH share the same page buffer. Writing to the NVM block via the AHB bus is performed by a load operation to the page buffer. For each AHB bus write, the address is stored in the ADDR register. After the page buffer has been loaded with the required number of bytes, the page can be written to the array pointed by ADDR by setting CTRLA.CMD to 'Write Page' and setting the key value to CMDEX. The LOAD bit in the STATUS register indicates whether the page buffer has been loaded or not.

If the NVMCTRL is busy processing a write command (STATUS.READY=0), then the AHB bus is stalled upon AHB write until the ongoing command completes.

The NVM Controller requires that an erase must be done before programming. Rows can be individually erased by the Erase Row command to erase a row.

Automatic page writes are enabled by writing the manual write bit to zero (CTRLC.MANW=0). This will trigger a write operation to the page addressed by ADDR when the last location of the page is written.

Because the address is automatically stored in ADDR during the APB bus write operation, the last given address will be present in the ADDR register. There is no need to load the ADDR register manually, unless a different page in memory is to be written. The page buffer is automatically cleared upon a 'Write Page' command completion.