8.1 Operation

Moving the interrupt vector table to the start of the boot section in Flash is enabled by writing '1' to the IVSEL bit in CPUINT.CTRLA. This system critical register bit has Configuration Change Protection (CCP) to prevent accidental modification. Refer to the CPU chapter in the relevant device data sheet for details on CCP.

Since the application section is placed after the boot section, the actual address of the interrupt vector table is determined by the BOOTEND fuse. This fuse sets the size of the boot section in blocks of 256 bytes. When IVSEL is set, the interrupt vector table will be at the start of Flash. Be aware that if both the BOOTEND fuse and APPEND fuse (size of application section) are set to 0x00 the entire Flash is configured to be the boot, and the interrupt vector table will be at the start of Flash.

The Reset vector address is 0x0000 (Start of Flash) in both IVSEL states. This corresponds with the lowest address in the boot interrupt vector table, which means the Reset vector will be the first instruction to execute after a reset has occurred.