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Clock Generator
Chapter 4
Preliminary User’s Manual U17566EE1V2UM00
Chapter 4 Clock Generator
The clock generator provides the clock signals needed by the CPU and the
on-chip peripherals.
4.1 Overview
The clock generator can generate the required clock signals from the following
sources:
• Main oscillator - a built-in oscillator with external crystal and a nominal
frequency of 4 MHz
• Sub oscillator - a built-in oscillator with external crystal and a nominal
frequency of 32 KHz
• Ring oscillator - an internal oscillator without external components and a
nominal frequency of 240 KHz
Features summary
Special features of the clock generator are:
• Choice of oscillators to reduce power consumption in stand-by mode
• Frequency multiplication by two PLL synthesizers:
– Fixed frequency PLL for accurate timings
– Spread spectrum PLL (SSCG) for reduced electromagnetic interference
• Individual clock source selection for CPU and groups of peripherals
• Five specific power save modes:
– HALT mode
– IDLE mode
– WATCH mode
– Sub-WATCH mode
– STOP mode
• Vital system registers are write-protected by a special write sequence
• Direct main oscillator clock feed-through for watch clock correction support
• Separate clock monitors for main and sub oscillator to detect oscillator
malfunction
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