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情况描述——
4路PWM输出，通过设置占空比，分别是50%，37.5%，25%，12.5%，用万用表观察单片机各个PWM引脚输出电压，分别是3.3V与上述比例相乘的值。
然后，分别将这4路与L298N的ENA端短接起来对比测试L298N输出电压，
发现到了L298N输出端测得的电压就不是这个比例了，除了50%的那路输出将近3V的电压(12V直流减速电机还能转动)，其余各路都接近于0V（电机不转）。
配置代码如下：
/*
* 函数名：TIM3_GPIO_Config
* 描述 ：配置TIM3复用输出PWM时用到的I/O
* 输入 ：无
* 输出 ：无
* 调用 ：内部调用
* 硬件连接：---------------------
* | PA.06: (TIM3_CH1) |
* | PA.07: (TIM3_CH2) |
* | PB.00: (TIM3_CH3) |
* | PB.01: (TIM3_CH4) |
* ---------------------
*/
static void TIM3_GPIO_Config(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/* TIM3 clock enable */
//PCLK1经过2倍频后作为TIM3的时钟源等于72MHz
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
/* GPIOA and GPIOB clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB, ENABLE);
/*GPIOA Configuration: TIM3 channel 1 and 2 as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 | GPIO_Pin_7;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; // 复用推挽输出
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/*GPIOB Configuration: TIM3 channel 3 and 4 as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1;
GPIO_Init(GPIOB, &GPIO_InitStructure);
}
/*
* 函数名：TIM3_Mode_Config
* 描述 ：配置TIM3输出的PWM信号的模式，如周期、极性、占空比
* 输入 ：无
* 输出 ：无
* 调用 ：内部调用
*/
static void TIM3_Mode_Config(void)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
/* PWM信号电平跳变值 */
u16 CCR1_Val = 500;
u16 CCR2_Val = 375;
u16 CCR3_Val = 250;
u16 CCR4_Val = 125;
/* -----------------------------------------------------------------------
TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
TIM3CLK = 72 MHz, Prescaler = 0x0, TIM3 counter clock = 72 MHz
TIM3 ARR Register = 999 => TIM3 Frequency = TIM3 counter clock/(ARR + 1)
TIM3 Frequency = 72 KHz.
TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
----------------------------------------------------------------------- */
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 999; //当定时器从0计数到999，即为1000次，为一个定时周期
TIM_TimeBaseStructure.TIM_Prescaler = 0; //设置预分频：不预分频，即为72MHz
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1 ; //设置时钟分频系数：不分频
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; //向上计数模式
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* PWM1 Mode configuration: Channel1 */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1; //配置为PWM模式1
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR1_Val; //设置跳变值，当计数器计数到这个值时，电平发生跳变
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; //当定时器计数值小于CCR1_Val时为高电平
TIM_OC1Init(TIM3, &TIM_OCInitStructure); //使能通道1
TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
/* PWM1 Mode configuration: Channel2 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR2_Val; //设置通道2的电平跳变值，输出另外一个占空比的PWM
TIM_OC2Init(TIM3, &TIM_OCInitStructure); //使能通道2
TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);
/* PWM1 Mode configuration: Channel3 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR3_Val; //设置通道3的电平跳变值，输出另外一个占空比的PWM
TIM_OC3Init(TIM3, &TIM_OCInitStructure); //使能通道3
TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);
/* PWM1 Mode configuration: Channel4 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR4_Val; //设置通道4的电平跳变值，输出另外一个占空比的PWM
TIM_OC4Init(TIM3, &TIM_OCInitStructure); //使能通道4
TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM3, ENABLE); // 使能TIM3重载寄存器ARR
/* TIM3 enable counter */
TIM_Cmd(TIM3, ENABLE); //使能定时器3
}
/*
* 函数名：TIM3_PWM_Init
* 描述 ：TIM3 输出PWM信号初始化，只要调用这个函数
* TIM3的四个通道就会有PWM信号输出
* 输入 ：无
* 输出 ：无
* 调用 ：外部调用
*/
void TIM3_PWM_Init(void)
{
TIM3_GPIO_Config();
TIM3_Mode_Config();
}
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发表于 2017-8-2 20:00:46
楼主