说明：  实现DAC数模转换，实现DAC数模转换，实现DAC数模转换，实现DAC数模转换实现DAC数模转换
( // The system is clocked by the internal 24.5MHz oscillator. The completion of // this conversion in turn triggers an interrupt service routine (ISR). The ISR // calculates the ADC0 result into the equivalent mV and then prints the value // to the terminal via printf before starting another conversion.)