These bits set the end of the application code section in blocks of 256 bytes. The end of the application code section should be set as BOOT size plus application code size. The remaining Flash will be application data. A value of 0x00 defines the Flash from BOOTEND*256 to the end of Flash as the application code section. When both FUSE.APPEND and FUSE.BOOTEND are 0x00 the entire Flash is BOOT section.