STM32裡的CAN 支援2.0A,2.0B, 帶有FIFO,中斷等, 這裡主要提一下內部的時鐘應用.

bxCAN掛接在APB1總線上,採用匯流排時鐘,所以我們需要知道APB1的匯流排時鐘是多少. 我們先看看下圖,看看APB1匯流排時鐘:

APB1時鐘取自AHB的分頻, 而AHB又取自系統時鐘的分頻, 系統時鐘可選HSI,HSE, PLLCLK, 這個在例程的RC設定裡都有的,

然後再看看有了APB1的時鐘後,如何算CAN的匯流排速率, 先看下圖:

有了上邊的這個圖,基本就清楚了.

                       匯流排時鐘MHz   (3+TS1+TS2)*(BRP+1)

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下面是我的計算：

CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;CAN_InitStructure.CAN_BS1 = CAN_BS1_3tq; 

注意//#define CAN_BS1_3tq                 ((uint8_t)0x02) /*!< 3 time quantum */CAN_InitStructure.CAN_BS2 = CAN_BS2_5tq;CAN_InitStructure.CAN_Prescaler = 4;//2nominal bit time（3+5+1）tq=9tq關於分頻係數 檢視 system_stm32f10x.c

所以can時鐘 72MHZ/2/4=9 Mhztq=1/36Mhz波特率為 1/nominal bit time= 9/9=1MHZ

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void CAN_Configuration(void) { CAN_InitTypeDef         CAN_InitStructure; CAN_FilterInitTypeDef   CAN_FilterInitStructure; /* CAN register init */ CAN_DeInit(); CAN_StructInit(&CAN_InitStructure); /* CAN cell init */ CAN_InitStructure.CAN_TTCM=DISABLE; CAN_InitStructure.CAN_ABOM=DISABLE; CAN_InitStructure.CAN_AWUM=DISABLE; CAN_InitStructure.CAN_NART=DISABLE; CAN_InitStructure.CAN_RFLM=DISABLE; CAN_InitStructure.CAN_TXFP=DISABLE; CAN_InitStructure.CAN_Mode=CAN_Mode_Normal; CAN_InitStructure.CAN_SJW=CAN_SJW_1tq; CAN_InitStructure.CAN_BS1=CAN_BS1_9tq; CAN_InitStructure.CAN_BS2=CAN_BS2_8tq; CAN_InitStructure.CAN_Prescaler=200; CAN_Init(&CAN_InitStructure); /* CAN filter init */ CAN_FilterInitStructure.CAN_FilterNumber=0; CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask; CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_16bit; CAN_FilterInitStructure.CAN_FilterIdHigh=0x0000; CAN_FilterInitStructure.CAN_FilterIdLow=0x0000; CAN_FilterInitStructure.CAN_FilterMaskIdHigh=0x0000; CAN_FilterInitStructure.CAN_FilterMaskIdLow=0x0000; CAN_FilterInitStructure.CAN_FilterFIFOAssignment=0; CAN_FilterInitStructure.CAN_FilterActivation=ENABLE; CAN_FilterInit(&CAN_FilterInitStructure); } 注意//#define CAN_BS1_3tq                 ((uint8_t)0x02) /*!< 3 time quantum */撥特率10K，公式：72MHZ/2/200/（1+9+8）=0.01，即10K，和SJA1000測試通過

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120歐姆電阻要加上！！！ 

哦確實是       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);    總結一下    Fpclk=36M 時 can波特率為250k   的配置為 /* CAN cell init */    CAN_InitStructure.CAN_TTCM=DISABLE;    CAN_InitStructure.CAN_ABOM=DISABLE;    CAN_InitStructure.CAN_AWUM=DISABLE;    CAN_InitStructure.CAN_NART=DISABLE;    CAN_InitStructure.CAN_RFLM=DISABLE;    CAN_InitStructure.CAN_TXFP=DISABLE;    CAN_InitStructure.CAN_Mode=CAN_Mode_LoopBack;    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=9;    CAN_Init(&CAN_InitStructure); 250k 

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的：將can匯流排波特率設定為250k 　在官方的can例程上 給出了100k 查詢 和500k 中斷方式的例子 分別設定如下：    CAN_Polling：    /* CAN cell init */    CAN_InitStructure.CAN_TTCM=DISABLE;    CAN_InitStructure.CAN_ABOM=DISABLE;    CAN_InitStructure.CAN_AWUM=DISABLE;    CAN_InitStructure.CAN_NART=DISABLE;    CAN_InitStructure.CAN_RFLM=DISABLE;    CAN_InitStructure.CAN_TXFP=DISABLE;    CAN_InitStructure.CAN_Mode=CAN_Mode_LoopBack;    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;    CAN_Init(&CAN_InitStructure); 100k    /* CAN cell init */    CAN_Interrupt    CAN_InitStructure.CAN_TTCM=DISABLE;    CAN_InitStructure.CAN_ABOM=DISABLE;    CAN_InitStructure.CAN_AWUM=DISABLE;    CAN_InitStructure.CAN_NART=DISABLE;    CAN_InitStructure.CAN_RFLM=DISABLE;    CAN_InitStructure.CAN_TXFP=DISABLE;    CAN_InitStructure.CAN_Mode=CAN_Mode_LoopBack;    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=1;    CAN_Init(&CAN_InitStructure); //500k 

can時鐘是RCC_APB1PeriphClock，你要注意CAN時鐘頻率 CAN波特率 = RCC_APB1PeriphClock/CAN_SJW+CAN_BS1+CAN_BS2/CAN_Prescaler; 如果CAN時鐘為8M， CAN_SJW = 1，CAN_BS1 = 8，CAN_BS2 = 7，CAN_Prescaler = 2 那麼波特率就是=8M/(1+8+7)/2=250K 

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得到500Kb/s的波特率

上邊這個公式算出來的就是CAN的速率了