官方库中利用TIM1产生7路PWM的例程，是否有错？

只看该作者 · 2011-8-16 10:12

00068 /* TIM1 Configuration ---------------------------------------------------

00069 Generate 7 PWM signals with 4 different duty cycles:

00070 TIM1CLK = SystemCoreClock, Prescaler = 0, TIM1 counter clock = SystemCoreClock

00071 SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density

00072 and Connectivity line devices and to 24 MHz for Low-Density Value line and

00073 Medium-Density Value line devices

00074 

00075 The objective is to generate 7 PWM signal at 17.57 KHz:

00076 - TIM1_Period = (SystemCoreClock / 17570) - 1

00077 The channel 1 and channel 1N duty cycle is set to 50%

00078 The channel 2 and channel 2N duty cycle is set to 37.5%

00079 The channel 3 and channel 3N duty cycle is set to 25%

00080 The channel 4 duty cycle is set to 12.5%

00081 The Timer pulse is calculated as follows:

00082 - ChannelxPulse = DutyCycle * (TIM1_Period - 1) / 100

00083 ----------------------------------------------------------------------- */

00084 /* Compute the value to be set in ARR regiter to generate signal frequency at 17.57 Khz */

00085 TimerPeriod = (SystemCoreClock / 17570 ) - 1;

00086 /* Compute CCR1 value to generate a duty cycle at 50% for channel 1 and 1N */

00087 Channel1Pulse = (uint16_t) (((uint32_t) 5 * (TimerPeriod - 1)) / 10);

00088 /* Compute CCR2 value to generate a duty cycle at 37.5% for channel 2 and 2N */

00089 Channel2Pulse = (uint16_t) (((uint32_t) 375 * (TimerPeriod - 1)) / 1000);

00090 /* Compute CCR3 value to generate a duty cycle at 25% for channel 3 and 3N */

00091 Channel3Pulse = (uint16_t) (((uint32_t) 25 * (TimerPeriod - 1)) / 100);

00092 /* Compute CCR4 value to generate a duty cycle at 12.5% for channel 4 */

00093 Channel4Pulse = (uint16_t) (((uint32_t) 125 * (TimerPeriod- 1)) / 1000);

这是官方库中利用TIM1产生7路PWM的例程。
此句计算定时器重加载的值TimerPeriod，已经有了减1
00085 TimerPeriod = (SystemCoreClock / 17570 ) - 1;
下句计算设置占空比为50%，其中在TimerPeriod的基础上又有减1，请问是否是个错误？还是另有原因？
00087 Channel1Pulse = (uint16_t) (((uint32_t) 5 * (TimerPeriod - 1)) / 10);