STM32_CAN波特率计算-网友总结

STM32 CAN 波特率 计算

CAN波特率计算—网友总结

STM32里的CAN 支持2.0A,2.0B, 带有FIFO,中断等, 这里主要提一下内部的时钟应用.

bxCAN挂接在APB1总线上,采用总线时钟,所以我们需要知道APB1的总线时钟是多少. 我们先看看下图,看看APB1总线时钟:

APB1时钟取自AHB的分频, 而AHB又取自系统时钟的分频, 系统时钟可选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,如何算CAN的总线速率, 先看下图:

STM32 CAN 波特率 计算

有了上边的这个图,基本就清楚了.

总线时钟MHz (3+TS1+TS2)*(BRP+1)

=================================================== 下面是我的计算：

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;//2

nominal bit time（3+5+1）tq=9tq

关于分频系数 查看 system_stm32f10x.c下面的

static void SetSysClockTo72(void) 函数

/* HCLK = SYSCLK */

/* PCLK2 = HCLK */

/* PCLK1 = HCLK/2 */

STM32 CAN 波特率 计算

所以can时钟 72MHZ/2/4=9 Mhz

tq=1/36Mhz

波特率为 1/nominal bit time= 9/9=1MHZ

=========================================

==================================================== 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

STM32 CAN 波特率 计算

quantum */

拨特率10K，公式：72MHZ/2/200/（1+9+8）=0.01，即10K，和SJA1000测试通过

================================================ 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 的配置为

/* 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

======================================

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 中断方式的例子 分别设置如下：

CAN_Polling：

STM32 CAN 波特率 计算

/* 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，你要注意CAN时钟频率 CAN波特率 =

RCC_APB1PeriphClock/CAN_SJW+CAN_BS1+CAN_BS2/CAN_Prescaler;

如果CAN时钟为8M， CAN_SJW = 1，CAN_BS1 = 8，CAN_BS2 = 7，CAN_Prescaler = 2

那么波特率就是=8M/(1+8+7)/2=250K

=========================================

得到500Kb/s的波特率

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;

STM32 CAN 波特率 计算

每一位的Tq数目 = 1 (固定SYNC_SEG) + 8 (BS1) + 7 (BS2) = 16

如果CAN时钟是 8 MHz : (8M / 1 ) / 16 = 5 …… 此处隐藏：3891字，全部文档内容请下载后查看。喜欢就下载吧 ……