Checksum

The pre-calculated checksum must be present in the last location of the section to be checked. If the BOOT section should be checked, the 16-bit checksum must be saved in the last two bytes of the BOOT section, and similarly for APPLICATION and entire Flash. Table 1 shows explicitly how the checksum should be stored for the different sections. Also, see the CRCSCAN.CTRLB register description for how to configure which section to check and the device fuse description for how to configure the BOOTEND and APPEND fuses.

Table 1. How to Place the Pre-Calculated 16-Bit Checksum in Flash
Section to Check CHECKSUM[15:8] CHECKSUM[7:0]
BOOT FUSE_BOOTEND*256-2 FUSE_BOOTEND*256-1
BOOT and APPLICATION FUSE_APPEND*256-2 FUSE_APPEND*256-1
Full Flash FLASHEND-1 FLASHEND