STM32的CAN波特率计算_转
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:
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 */
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 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:
/* 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
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