Different fields in a register might have different access permissions enforced by hardware.
The access permission for each register field is documented in the Access column in the following ways:
| Access | Description | Hardware behavior |
|---|---|---|
| R | Read-only | Field can only be read. A write will be ignored. |
| W | Write-only | Field can only be written. A read will return an undefined value. |
| RW | Read-write | Field can be read and written multiple times. |
| W1 | Write-once | Field can only be written once per reset. Any subsequent write will be ignored. A read will return an undefined value. |
| RW1 | Read-write-once | Field can be read multiple times, but only written once per reset. Any subsequent write will be ignored. |
| W0C | Write 0 to clear | Field can be read multiple times. A zero clears (set to zero) the corresponding bit in the register. Bits set to one are ignored. |
| W1C | Write 1 to clear | Field can be read multiple times. A one clears (set to zero) the corresponding bit in the register. Bits set to zero are ignored. |
| W1S | Write 1 to set | Field can be read multiple times. A one sets the corresponding bit in the register. Bits set to zero are ignored. |
| RME | Read Modify External | When read, a side effect occurs. |