采样法生成三相SPWM波的开环调速控制程序载波频率为20KHz，或载波周期为50μs。DSP晶振10MHz，内部4倍频，时钟频率为40MHz，计数周期为25ns。假设调制波频率由外部输入（1～50Hz），并转换成合适的格式-Sampling method to generate three-phase SPWM wave open-loop speed control procedures for the carrier frequency 20KHz, or carrier period is