关于PWM占空比的一些问题

Iwaly · 发表于 2017-10-17 21:10:39

TIM4_PWM_Init(7199,0);
......
void SetMotorSpeed(unsigned char ucChannel,signed char cSpeed)
{
//  static short sMotorSpeed = 0;
  short sPWM;
// float fDir = 1;

  if (cSpeed>=100) cSpeed = 100;
if (cSpeed<=-100) cSpeed = -100;

sPWM = 3600 - fabs(cSpeed)*72;
switch(ucChannel)
{
  case 0:
TIM_SetCompare3(TIM4,sPWM);
......

TIM_ TIM_SetCompare3  这个函数什么意思？为什么调节SPWM的值能改变占空比，spwm的值为什么要是负数？