AN663
features a highly configurable clock structure. The advanced highperformance bus (AHB) and advanced peripheral bus (APB) have many options available for clocking. In addition, firmware can disable most peripheral clocks to save power. The clock to the module must be enabled before firmware can modify the registers. The first initialization step in all peripheral initialization routines should enable the clock to the module. The corresponding Precision32 family reference manual contains detailed descriptive and usage information on each of the clock sources mentioned in this document.
2. Clock Sources
The AHB drives the core and memory on ARM® Cortex™-M3 devices. The APB drives the peripherals and peripheral registers. The AHB on the Precision32 devices has several options for clock sources: Low Power Oscillator, Low Frequency Oscillator, RTC Oscillator, External Oscillator, PLL Oscillator, and USB Oscillator. The APB clock is either equal to AHB or a divide by 2 version of it, so it...
