SAM D21/DA1 Family

32.5.8 Register Access Protection

Registers with write-access can be optionally write-protected by the Peripheral Access Controller (PAC), except for the following:

Device Interrupt Flag (INTFLAG) register
Endpoint Interrupt Flag (EPINTFLAG) register
Host Interrupt Flag (INTFLAG) register
Pipe Interrupt Flag (PINTFLAG) register

Note: Optional write-protection is indicated by the "PAC Write-Protection" property in the register description.

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

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