1.前言
OSC模块是一个晶体振荡器。 该模块使用晶体或谐振器与外部连接，为MCU产生一个参考时钟。
主要为下图红色框住的部分
2.特性和模式
Supports 32 kHz crystals (Low Range mode)
• Supports 3–8 MHz, 8–32 MHz crystals and resonators (High Range mode)
• Automatic Gain Control (AGC) to optimize power consumption in high frequency
ranges 3–8 MHz, 8–32 MHz using low-power mode
• High gain option in frequency ranges: 32 kHz, 3–8 MHz, and 8–32 MHz
• Voltage and frequency filtering to guarantee clock frequency and stability
• Optionally external input bypass clock from EXTAL signal directly
• One clock for MCU clock system
• Two clocks for on-chip peripherals that can work in Stop modes
3.框图
OCC模块使用晶振产生三个滤波后的晶振时钟信号：
1. OSCCLK:用于MCU
2.OSC32KCLK:
3.OSCERCLK:用于片上外设
OSCERCLK和OSC32KCLK可以工作在低功耗模式
4.OSC信号描述
5.外部晶振连接
6. 外部clock连接
7. Memory Map/Register Definitions
TODO