Datasheet

Table Of Contents

13.2 Synchronous and Asynchronous Clocks

As the CPU and the peripherals can be in different clock domains, i.e. they are clocked from different

clock sources and/or with different clock speeds, some peripheral accesses by the CPU need to be

synchronized. In this case the peripheral includes a Synchronization Busy (SYNCBUSY) register that can

be used to check if a sync operation is in progress.

For a general description, see 13.3 Register Synchronization. Some peripherals have specific properties

described in their individual sub-chapter “Synchronization”.

In the datasheet, references to Synchronous Clocks are referring to the CPU and bus clocks (MCLK),

while asynchronous clocks are generated by the Generic Clock Controller (GCLK).

Related Links

14.6.6 Synchronization

13.3 Register Synchronization

13.3.1 Overview

All peripherals are composed of one digital bus interface connected to the APB or AHB bus and running

from a corresponding clock in the Main Clock domain, and one peripheral core running from the

peripheral Generic Clock (GCLK).

Communication between these clock domains must be synchronized. This mechanism is implemented in

hardware, so the synchronization process takes place even if the peripheral generic clock is running from

the same clock source and on the same frequency as the bus interface.

All registers in the bus interface are accessible without synchronization.

All registers in the peripheral core are synchronized when written. Some registers in the peripheral core

are synchronized when read.

Each individual register description will have the properties "Read-Synchronized" and/or "Write-

Synchronized" if a register is synchronized.

As shown in the figure below, each register that requires synchronization has its individual synchronizer

and its individual synchronization status bit in the Synchronization Busy register (SYNCBUSY).

Note: For registers requiring both read- and write-synchronization, the corresponding bit in SYNCBUSY

is shared.

SAM D5x/E5x Family Data Sheet

Clock System

Datasheet

DS60001507E-page 147