5.1.4 Clock Prescaling

Many applications require the CPU operating as fast as possible to minimize the time spent in active mode. But, for certain applications, the CPU has to wait in Active or Idle mode for a fixed amount of time (e.g. serial communication), where it is better to reduce the system clock rate. In these cases, it is better to configure the appropriate CPU and peripheral clock frequencies using clock prescaling. If prescaling is done internally in several peripherals, power can be conserved by prescaling with the largest common factor as early as possible in the clock distribution chain.