TM4C1294输出PWM，修改不了占空比

Eruroraito

Expert 1136 points

先附上代码：

// 使能M0PWM外设

MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);

// PWM不分频

MAP_SysCtlPWMClockSet(SYSCTL_PWMDIV_1);

// Configure the PWM0 to count down without synchronization

// 配置GEN3递减计数模式不同步模式

PWMGenConfigure(PWM0_BASE,PWM_GEN_3,PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);

// 设置PWM周期

// N=(1/f)*SysClk,f is the desired frequency

PWMGenPeriodSet(PWM0_BASE,PWM_GEN_3,100);

// 设置PWM占空比

// Default 50%

PWMPulseWidthSet(PWM0_BASE,PWM_OUT_7,50);

// 使能PWM输出状态

PWMOutputState(PWM0_BASE,PWM_OUT_7_BIT,true);

// 使能PWM发生器

PWMGenEnable(PWM0_BASE,PWM_GEN_3);

这种情况下（SYSCLK:120M）：

1、其他都不变，更改占空比，示波器查看正常；

2、其他都不会，修改PWM分频为MAP_SysCtlPWMClockSet(SYSCTL_PWMDIV_64);，示波器查看的周期没变；

3、其他都不变，修改周期100为30000，示波器查看的波形周期正常4K，但是占空比却不是50%，继续更改占空比为80，也没效果，占空比很小；

综上，就是1、修改分频没效果；2、更改了周期100数字之后，占空没有输出预期值。初次涉及TM4C的芯片，有很多不懂的，不知道我这个问题出在哪了，谢谢

大家指点指点。

9 年多前

0 Maka Luo 9 年多前

TI__Genius 12740 points

// 设置PWM周期

// N=(1/f)*SysClk,f is the desired frequency

PWMGenPeriodSet(PWM0_BASE,PWM_GEN_3,3000);

// 设置PWM占空比

// Default 50%

PWMPulseWidthSet(PWM0_BASE,PWM_OUT_7,1500); //如果占空比是50%，这个值应该是1500/3000 而不是50.

也可以参照TI官方例程写法，如下：

//
// Set the PWM period to 250Hz. To calculate the appropriate parameter
// use the following equation: N = (1 / f) * SysClk. Where N is the
// function parameter, f is the desired frequency, and SysClk is the
// system clock frequency.
// In this case you get: (1 / 250Hz) * 16MHz = 64000 cycles. Note that
// the maximum period you can set is 2^16 - 1.
// TODO: modify this calculation to use the clock frequency that you are
// using.
//
PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, 64000);

//
// Set PWM0 PD0 to a duty cycle of 25%. You set the duty cycle as a
// function of the period. Since the period was set above, you can use the
// PWMGenPeriodGet() function. For this example the PWM will be high for
// 25% of the time or 16000 clock cycles (64000 / 4).
//
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0,PWMGenPeriodGet(PWM0_BASE, PWM_OUT_0) / 4); //这个是配置25%占空比的方法

//
// Enable the dead-band generation on the PWM0 output signal. PWM bit 0
// (PD0), will have a duty cycle of 25% (set above) and PWM bit 1 will have
// a duty cycle of 75%. These signals will have a 10us gap between the
// rising and falling edges. This means that before PWM bit 1 goes high,
// PWM bit 0 has been low for at LEAST 160 cycles (or 10us) and the same
// before PWM bit 0 goes high. The dead-band generator lets you specify
// the width of the "dead-band" delay, in PWM clock cycles, before the PWM
// signal goes high and after the PWM signal falls. For this example we
// will use 160 cycles (or 10us) on both the rising and falling edges of
// PD0. Reference the datasheet for more information on dead-band
// generation.
//

0 Maka Luo 9 年多前

TI__Genius 12740 points

如果周期改为30000， 50%占空比，其占空比配置为15000。

0 Eruroraito 9 年多前回复 Maka Luo

Expert 1136 points

谢谢大神，完美解决了问题。

就是有一点，PWMGenPeriodGet(PWM0_BASE, PWM_OUT_0) / 4，这个官方历程函数用的有问题，申明函数是这样的：PWMGenPeriodGet（uint32_t u32Base, uint32_t u32Gen）。

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TM4C1294输出PWM，修改不了占空比