ATtiny1617/3217

9.3.6 Configuration Change Protection

This peripheral has registers that are under Configuration Change Protection (CCP). In order to write to these, a certain key must be written to the CPU.CCP register first, followed by a write access to the protected bits within four CPU instructions.

Attempting to write to a protected register without following the appropriate CCP unlock sequence leaves the protected register unchanged.

The following registers are under CCP:

Table 9-4. NVMCTRL - Registers under Configuration Change Protection
Register	Key
NVMCTRL.CTRLA	SPM

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