37.5.8 Register Access Protection

All registers with write-access are optionally write-protected by the Peripheral Access Controller (PAC), except the following registers:

Control A (CTRLA) register
Transmit Data (TXDATA) register
Interrupt Flag Status and Clear (INTFLAG) register
Interrupt Flag Status and Clear (INTFLAG) register

PAC write-protection is denoted by the `'PAC Write-Protection' property in the register description.

Write-protection does not apply to accesses through an external debugger.

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