30.3.4 Configuration Change Protection

This peripheral has registers that can be placed under Configuration Change Protection (CCP) by writing a ‘1’ to the CCP bit in the CTRLA register. CCP is a security mechanism to prevent unintentional changes to the SWDT settings. To write to one of these protected registers, write a given key to the CPU’s CCP register and follow it by a write access to the protected register within four CPU instructions.

Attempting to write to a protected register without following the appropriate CCP unlock sequence leaves the protected register unchanged and returns a Bus Error on the data bus.

Writing a ‘1’ to the CCP bit in the CTRLA register sets the following registers under CCP.