Register Access Protection

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

Interrupt Flag Status and Clear register (INTFLAG)

Optional write-protection by the Peripheral Access Controller (PAC) is denoted by the "PAC Write-Protection" property in each individual register description.

When TrustZone is supported (SAM L11 only), all register reads are allowed. Non-secure writes to APB registers are limited as follows. Illegal writes will be ignored.

Some commands written to CTRLA such as Write/Erase and Lock/Unlock are only permitted to non-secure application and data space.
Writes to all other registers except CTRLC and INTFLAG are not allowed.