脉冲宽度调制PWM（Pulse Width Modulation），调理占空比以操控脉冲宽度。
STM32的定时器除了TIM6和TIM7，其它定时器都可以用来发生PWM信号，高档定时器TIM1和TIM8可一起发生7路PWM输出，通用定时器可一起发生4路PWM输出。
STM32定时器PWM输出设置的几个过程如下：
1）敞开STM32时钟，装备输出I/O为复用输出
2）设置ARR（周期）和PSC（预分频）
3）设置PWM形式（边缘对齐或中心对齐）
4）使能定时器的通道输出，使能定时器
5）修正CCR2来操控占空比
例程：72MHz主频，PB7（TIM4_CH2）输出PWM
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;// for PWM
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_Init(GPIOB, &GPIO_InitStructure);
void TIM4_Configuration(void)// for PWM
{
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);
TIM4->ARR = 900; // 设定计数器主动重装值 72MHz/900 = 8kHz
TIM4->PSC = 0; // 预分频器不分频
TIM4->CCMR1 |= 7<<12; // PWM2
TIM4->CCMR1 |= 1<<11; // CH2预装载使能
TIM4->CCER |= 1<<4; // OC2输出使能
TIM4->CR1 |= 0x8000; // ARPE使能
TIM4->CR1 |= 0x01; // 使能定时器
TIM4->CCR2 = 550; // 调理占空比
}
因IAR固件库每个版别不同，该例程直接对寄存器进行操控，以便利了解。
弥补一个根据固件库的例程（以TIM3为例，省掉IO设置部分）：
void TIM3_Configuration(void)
{
// 输出两路PWM
/*———————————————————-
RCC_APB2PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
TIM3->ARR = 900;// 最大900
TIM3->PSC = 0;
TIM3->CCMR1 |= 7<<12;// PWM2 中心对齐
TIM3->CCMR1 |= 1<<11;// CH2预装载使能
TIM3->CCER |= 1<<4;// OC2输出使能
TIM3->CCMR1 |= 7<<4;// PWM2 中心对齐
TIM3->CCMR1 |= 1<<3;// CH1预装载使能
TIM3->CCER |= 1;// OC1输出使能
TIM3->CR1 |= 0x8000;// ARPE使能
TIM3->CR1 |= 0x01;// 使能定时器
TIM3->CCR1 = 100;// 调理占空比TIM3_CH1
TIM3->CCR2 = 300;// 调理占空比TIM3_CH2
———————————————————–*/
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
TIM_TimeBaseStructure.TIM_Period = 999;
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* PWM1 Mode configuration: Channel1 */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 500;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init(TIM3, &TIM_OCInitStructure);
TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
/* PWM1 Mode configuration: Channel2 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 300;
TIM_OC2Init(TIM3, &TIM_OCInitStructure);
TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM3, ENABLE);
TIM_Cmd(TIM3, ENABLE);
}
