6.9 Oscillator and System Clock

The clock system is supported by the Basic Clock module that includes support for an internal digitally controlled oscillator (DCO), a high-frequency crystal oscillator, and an internal very-low-power low-frequency oscillator (VLO). The clock module is designed to meet the requirements of both low system cost and low power consumption. The internal DCO provides a fast turnon clock source and stabilizes in less than 1 µs. The clock module provides the following clock signals:

• Auxiliary clock (ACLK), sourced from the VLO
• Main clock (MCLK), the system clock used by the CPU
• Sub-Main clock (SMCLK), the subsystem clock used by the peripheral modules

Table 6-8 lists the addresses of the available DCO calibration data.