STM32F0X CAN波特率问题

1万 · 2021-11-21 15:41

采用内部晶振8M，6倍PLL主频48M，配置250K波特率，实际示波器抓的怎么和预期不符？估算少了6倍？
这是配置代码：
      //CAN speed = (48M) / CAN_Prescaler / (1+BS1+BS2) = 48000000/32/6 = 250K
      CAN_InitStructure.CAN_SJW=CAN_SJW_1tq;       // 1tq、BS1、BS2的值跟波特率有关
      CAN_InitStructure.CAN_BS1=CAN_BS1_3tq;
      CAN_InitStructure.CAN_BS2=CAN_BS2_2tq;
      CAN_InitStructure.CAN_Prescaler=32;                                        // 分频系数为32
      CAN_Init(CAN, &CAN_InitStructure);                                              // 初始化CAN1

1万 · 2021-11-21 15:44

如果系统时钟48MHz的话，根据你的配置应该是250K.

1万 · 2021-11-21 15:48

1万 · 2021-11-21 15:51

整整差6倍，会不会你PLL根本没起作用？

1万 · 2021-11-21 15:53

还是说测错了？

1万 · 2021-11-21 15:56

示波器找一个最窄方波测量宽度，这应该就是一个bit啊，PLL不会错啊

1万 · 2021-11-21 15:58

这是PLL设定代码：
  if (HSEStatus == (uint32_t)0x01)
  {
/* Enable Prefetch Buffer and set Flash Latency */
FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;

/* HCLK = SYSCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

/* PCLK = HCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;

/* PLL configuration = HSE * 6 = 48 MHz */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_PREDIV1 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL6);

/* Enable PLL */
RCC->CR |= RCC_CR_PLLON;

/* Wait till PLL is ready */
while((RCC->CR & RCC_CR_PLLRDY) == 0)
{
}

/* Select PLL as system clock source */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;

/* Wait till PLL is used as system clock source */
while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
{
}
  }