11.3.5 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 11-2. CLKCTRL - Registers Under Configuration Change Protection
Register Key
CLKCTRL.MCLKCTRLB IOREG
CLKCTRL.MCLKLOCK IOREG
CLKCTRL.XOSC32KCTRLA IOREG
CLKCTRL.MCLKCTRLA IOREG
CLKCTRL.OSC20MCTRLA IOREG
CLKCTRL.OSC20MCALIBA IOREG
CLKCTRL.OSC20MCALIBB IOREG
CLKCTRL.OSC32KCTRLA IOREG