51.6.10 Synchronization

Due to asynchronicity between the main clock domain and the peripheral clock domains, some registers need to be synchronized when written or read.

When executing an operation that requires synchronization, the corresponding Synchronization Busy bit in the Synchronization Busy register (SYNCBUSY) will be set immediately, and cleared when synchronization is complete.

If an operation that requires synchronization is executed while the corresponding SYNCBUSY bit is '1', a peripheral bus error is generated.

The following bits are synchronized when written:

  • Software Reset bit in the Control A register (CTRLA.SWRST). SYNCBUSY.SWRST is set to '1' while synchronization is in progress.
  • Enable bit in the Control A register (CTRLA.ENABLE). SYNCBUSY.ENABLE is set to '1' while synchronization is in progress.
  • Clock Unit x Enable bits in the Control A register (CTRLA.CKENx). SYNCBUSY.CKENx is set to '1' while synchronization is in progress.
  • Serializer Enable bits in the Control A register (CTRLA.TXEN and CTRLA.RXEN). SYNCBUSY.TXEN/RXEN is set to '1' while synchronization is in progress.
The following registers require synchronization when read or written:
  • Transmit Data register (TXDATA) is Write-Synchronized. SYNCBUSY.TXDATA is set to '1' while synchronization is in progress.
  • Receive Data register (RXDATA) is Read-Synchronized. SYNCBUSY.RXDATA is set to '1' while synchronization is in progress.

Synchronization is denoted by the Read-Synchronized or Write-Synchronized property in the register description.