14
XMEGA B [DATASHEET]
8291B–AVR–01/2013
3.12.2 Sequence for execution of protected SPM/LPM
1.
The application code writes the signature for the execution of protected SPM/LPM to the CCP register.
2.
Within four instruction cycles, the application code must execute the appropriate instruction. The protected change
is immediately disabled if the CPU performs write operations to the data memory or if the SLEEP instruction is
executed.
Once the correct signature is written by the CPU, interrupts will be ignored for the duration of the configuration change
enable period. Any interrupt request (including non-maskable interrupts) during the CCP period will set the
corresponding interrupt flag as normal, and the request is kept pending. After the CCP period is completed, any pending
interrupts are executed according to their level and priority. DMA requests are still handled, but do not influence the
protected configuration change enable period. A signature written by DMA is ignored.
3.13
Fuse Lock
For some system-critical features, it is possible to program a fuse to disable all changes to the associated I/O control
registers. If this is done, it will not be possible to change the registers from the user software, and the fuse can only be
reprogrammed using an external programmer. Details on this are described in the datasheet module where this feature is
available.
Summary of Contents for XMEGA B
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