15.5.2.4 Selecting the Synchronous Clock Division Ratio

The main clock GCLK_MAIN feeds an 8-bit prescaler, which can be used to generate the synchronous clocks. By default, the synchronous clocks run on the undivided main clock. The user can select a prescaler division for the CPU clock domain by writing the Division (DIV) bits in the CPU Clock Division register CPUDIV, resulting in a CPU clock domain frequency determined by this equation:

f_{C P U} = \frac{f_{m a i n}}{C P U D I V}

If the application attempts to write forbidden values in the CPUDIV register, the register is written but these bad values are not used and a violation is reported to the PAC module.

Division bits (DIV) can be written without halting or disabling peripheral modules. Writing DIV bits allows a new clock setting to be written to all synchronous clocks belonging to the corresponding clock domain at the same time.

Figure 15-2. Synchronous Clock Selection and Prescaler