STM32的CAN波特率核算_转

STM32里的CAN 支撑2.0A,2.0B, 带有FIFO,中止等, 这儿首要提一下内部的时钟运用.

bxCAN挂接在APB1总线上,选用总线时钟,所以咱们需求知道APB1的总线时钟是多少. 咱们先看看下图,看看APB1总线时钟:

APB1时钟取自AHB的分频, 而AHB又取自体系时钟的分频, 体系时钟可选HSI,HSE, PLLCLK, 这个在例程的RC设置里都有的,

然后再看看有了APB1的时钟后,怎么算CAN的总线速率, 先看下图:

有了上边的这个图,基本就清楚了.

总线时钟MHz (3+TS1+TS2)*(BRP+1)

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下面是我的核算：

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

留意//#define CAN_BS1_3tq ((uint8_t)0x02) /*!< 3 time quantum */
CAN_InitStructure.CAN_BS2 = CAN_BS2_5tq;
CAN_InitStructure.CAN_Prescaler = 4;//2
nominal bit time（3+5+1）tq=9tq
关于分频系数 检查 system_stm32f10x.c下面的
static void SetSysClockTo72(void) 函数
/* HCLK = SYSCLK */
/* PCLK2 = HCLK */
/* PCLK1 = HCLK/2 */

所以can时钟 72MHZ/2/4=9 Mhz
tq=1/36Mhz
波特率为 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);
}
留意//#define CAN_BS1_3tq ((uint8_t)0x02) /*!< 3 time quantum */
拨特率10K，公式：72MHZ/2/200/（1+9+8）=0.01，即10K，和SJA1000测试通过

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120欧姆电阻要加上！！！

哦 确实是

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);

总结一下
Fpclk=36M 时 can波特率为250k 的装备为

/* 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：将can总线波特率设置为250k
　　
　在官方的can例程上 给出了100k 查询 和500k 中止方法的比如 别离设置如下：
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时钟是RCC_APB1PeriphClock，你要留意CAN时钟频率
CAN波特率 = RCC_APB1PeriphClock/CAN_SJW+CAN_BS1+CAN_BS2/CAN_Prescaler;
假如CAN时钟为8M， CAN_SJW = 1，CAN_BS1 = 8，CAN_BS2 = 7，CAN_Prescaler = 2
那么波特率便是=8M/(1+8+7)/2=250K

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得到500Kb/s的波特率

上边这个公式算出来的便是CAN的速率了.