can拨特率计算？

只看该作者 · 2009-3-4 16:35

我算的怎么和例子上的不一样啊？例子上的100KBPS/S：设置如下（用的外部晶振（是8M的吗？），SYSCLK是HSE，CAN时钟应该是4M吧！

  CAN_InitStructure.CAN_SJW=CAN_SJW_1tq;
  CAN_InitStructure.CAN_BS1=CAN_BS1_8tq;
  CAN_InitStructure.CAN_BS2=CAN_BS2_7tq;
  CAN_InitStructure.CAN_Prescaler=5;

  if(HSEStartUpStatus == SUCCESS)
  {
    /* HCLK = SYSCLK */
    RCC_HCLKConfig(RCC_SYSCLK_Div1);

    /* PCLK2 = HCLK */
    RCC_PCLK2Config(RCC_HCLK_Div1);

    /* PCLK1 = HCLK/2 */
    RCC_PCLK1Config(RCC_HCLK_Div2);

    /* Enable Prefetch Buffer */
    FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

    /* Select HSE as system clock source */
    RCC_SYSCLKConfig(RCC_SYSCLKSource_HSE);

    /* Wait till HSE is used as system clock source */
    while(RCC_GetSYSCLKSource() != 0x04)
    {
    }

只看该作者 · 2009-3-5 08:50

  CAN_InitStructure.CAN_BS1=CAN_BS1_8tq;
  CAN_InitStructure.CAN_BS2=CAN_BS2_7tq;
  CAN_InitStructure.CAN_Prescaler=5;

上面参数设置CAN寄存器，要得到100KPS/S的拨特率，CAN时钟应该是18MHZ吧？

只看该作者 · 2009-3-5 09:42

stm32f10x_can.h:

/* CAN synchronisation jump width */
#define CAN_SJW_1tq                 ((u8)0x00)  /* 1 time quantum */
#define CAN_SJW_2tq                 ((u8)0x01)  /* 2 time quantum */
#define CAN_SJW_3tq                 ((u8)0x02)  /* 3 time quantum */
#define CAN_SJW_4tq                 ((u8)0x03)  /* 4 time quantum */

#define IS_CAN_SJW(SJW) (((SJW) == CAN_SJW_1tq) || ((SJW) == CAN_SJW_2tq)||
                         ((SJW) == CAN_SJW_3tq) || ((SJW) == CAN_SJW_4tq))

/* time quantum in bit segment 1 */
#define CAN_BS1_1tq                 ((u8)0x00)  /* 1 time quantum */
#define CAN_BS1_2tq                 ((u8)0x01)  /* 2 time quantum */
#define CAN_BS1_3tq                 ((u8)0x02)  /* 3 time quantum */
#define CAN_BS1_4tq                 ((u8)0x03)  /* 4 time quantum */
#define CAN_BS1_5tq                 ((u8)0x04)  /* 5 time quantum */
#define CAN_BS1_6tq                 ((u8)0x05)  /* 6 time quantum */
#define CAN_BS1_7tq                 ((u8)0x06)  /* 7 time quantum */
#define CAN_BS1_8tq                 ((u8)0x07)  /* 8 time quantum */
#define CAN_BS1_9tq                 ((u8)0x08)  /* 9 time quantum */
#define CAN_BS1_10tq                ((u8)0x09)  /* 10 time quantum */
#define CAN_BS1_11tq                ((u8)0x0A)  /* 11 time quantum */
#define CAN_BS1_12tq                ((u8)0x0B)  /* 12 time quantum */
#define CAN_BS1_13tq                ((u8)0x0C)  /* 13 time quantum */
#define CAN_BS1_14tq                ((u8)0x0D)  /* 14 time quantum */
#define CAN_BS1_15tq                ((u8)0x0E)  /* 15 time quantum */
#define CAN_BS1_16tq                ((u8)0x0F)  /* 16 time quantum */

#define IS_CAN_BS1(BS1) ((BS1) <= CAN_BS1_16tq)

/* time quantum in bit segment 2 */
#define CAN_BS2_1tq                 ((u8)0x00)  /* 1 time quantum */
#define CAN_BS2_2tq                 ((u8)0x01)  /* 2 time quantum */
#define CAN_BS2_3tq                 ((u8)0x02)  /* 3 time quantum */
#define CAN_BS2_4tq                 ((u8)0x03)  /* 4 time quantum */
#define CAN_BS2_5tq                 ((u8)0x04)  /* 5 time quantum */
#define CAN_BS2_6tq                 ((u8)0x05)  /* 6 time quantum */
#define CAN_BS2_7tq                 ((u8)0x06)  /* 7 time quantum */
#define CAN_BS2_8tq                 ((u8)0x07)  /* 8 time quantum */

stm32f10x_can.c :

/* Set the bit timing register */
    CAN->BTR = (u32)((u32)CAN_InitStruct->CAN_Mode << 30) | ((u32)CAN_InitStruct->CAN_SJW << 24) |
               ((u32)CAN_InitStruct->CAN_BS1 << 16) | ((u32)CAN_InitStruct->CAN_BS2 << 20) |
               ((u32)CAN_InitStruct->CAN_Prescaler - 1);

  CAN_InitStructure.CAN_BS1=CAN_BS1_8tq;
  CAN_InitStructure.CAN_BS2=CAN_BS2_7tq;
  CAN_InitStructure.CAN_Prescaler=5;

上面参数设置CAN寄存器，要得到100KPS/S的拨特率，CAN时钟应该是18MHZ吧？

由此推断, CAN时钟应该是 8 MHz ( 使用 HSE 8MHz, PLL 不使用 ? )

8M / 5 / ( 1+ 8 + 7 ) = 100 K

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只看该作者 · 2009-3-5 10:27

谢谢你！不过CAN的时钟是APB1啊，例子上：

    /* PCLK1 = HCLK/2 */
    RCC_PCLK1Config(RCC_HCLK_Div2);
   RCC_SYSCLKConfig(RCC_SYSCLKSource_HSE);

    /* Wait till HSE is used as system clock source */
    while(RCC_GetSYSCLKSource() != 0x04)
    {
    }

  外部晶振是8MHZ，CAN时钟应该是4MHZ啊