STM32: CAN bus communication-initialization/baud rate

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One, CAN bus communication initialization configuration

1. CAN bus communication initialization configuration process

1. CAN bus GPIO and clock configuration
2. CAN bus RX0 interrupt priority configuration
3. CAN bus initialization configuration

2. CAN bus GPIO and clock configuration

CAN pin configuration:


CAN clock configuration: the


specific code is as follows:

/*CAN GPIO 和时钟配置 */
void CAN_GPIO_Config(void)
{
    
    
	GPIO_InitTypeDef GPIO_InitStructure; 
	// 复用前先初始化GPIOB端口时钟，白的查了两天电路 
	/* 复用功能和GPIOB端口时钟使能*/	 
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO | RCC_APB2Periph_GPIOB, ENABLE);	                        											 

	/* CAN1 模块时钟使能 */
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_CAN1, ENABLE); 

	/* Configure CAN pin: RX */	 // PB8
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;	 // 上拉输入
	GPIO_Init(GPIOB, &GPIO_InitStructure);
  
	/* Configure CAN pin: TX */   // PB9
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; // 复用推挽输出
	GPIO_Init(GPIOB, &GPIO_InitStructure);
  
	//#define GPIO_Remap_CAN    GPIO_Remap1_CAN1 
	GPIO_PinRemapConfig(GPIO_Remap1_CAN1, ENABLE);  
}

3. CAN bus RX0 interrupt priority configuration

The specific code is as follows:

/*CAN RX0 中断优先级配置  */
void CAN_NVIC_Configuration(void) 
 {
    
    
    NVIC_InitTypeDef NVIC_InitStructure;
  	/* Configure the NVIC Preemption Priority Bits */  
  	NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);

	/* enabling interrupt */
  	NVIC_InitStructure.NVIC_IRQChannel=USB_LP_CAN1_RX0_IRQn;;
  	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  	NVIC_Init(&NVIC_InitStructure);
}

4. CAN bus initialization configuration

The specific code is as follows:

void CAN_INIT(void) 
{
    
    
	CAN_GPIO_Config();	//CAN管脚初始化
	CAN_NVIC_Configuration(); //CAN中断初始化  
	
	CAN_InitTypeDef        CAN_InitStructure;
	CAN_FilterInitTypeDef  CAN_FilterInitStructure;
	/* CAN register init */
	CAN_DeInit(CAN1);	//将外设CAN的全部寄存器重设为缺省值
	CAN_StructInit(&CAN_InitStructure);//把CAN_InitStruct中的每一个参数按缺省值填入

	/* CAN cell init */
	CAN_InitStructure.CAN_TTCM=DISABLE;//没有使能时间触发模式
	CAN_InitStructure.CAN_ABOM=DISABLE;//没有使能自动离线管理
	CAN_InitStructure.CAN_AWUM=DISABLE;//没有使能自动唤醒模式
	CAN_InitStructure.CAN_NART=DISABLE;//没有使能非自动重传模式
	CAN_InitStructure.CAN_RFLM=DISABLE;//没有使能接收FIFO锁定模式
	CAN_InitStructure.CAN_TXFP=DISABLE;//没有使能发送FIFO优先级
	CAN_InitStructure.CAN_Mode=CAN_Mode_Normal;	//CAN设置为正常模式
	CAN_InitStructure.CAN_SJW=CAN_SJW_1tq; 		//重新同步跳跃宽度1个时间单位
	CAN_InitStructure.CAN_BS1=CAN_BS1_3tq; 		//时间段1为3个时间单位
	CAN_InitStructure.CAN_BS2=CAN_BS2_2tq; 		//时间段2为2个时间单位
	CAN_InitStructure.CAN_Prescaler=24;  		//时间单位长度为24	   250k
	CAN_Init(CAN1,&CAN_InitStructure);
                                      		//波特率为：36M/24(1+3+2)=0.25 即250K

	/* CAN filter init */
	CAN_FilterInitStructure.CAN_FilterNumber=1;//指定过滤器为1
	CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask;//指定过滤器为标识符屏蔽位模式
	CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;//过滤器位宽为32位
	CAN_FilterInitStructure.CAN_FilterIdHigh=0x0000;// 过滤器标识符的高16位值
	CAN_FilterInitStructure.CAN_FilterIdLow=0x0000;//	 过滤器标识符的低16位值
	CAN_FilterInitStructure.CAN_FilterMaskIdHigh=0x0000;//过滤器屏蔽标识符的高16位值
	CAN_FilterInitStructure.CAN_FilterMaskIdLow=0x0000;//	过滤器屏蔽标识符的低16位值
	CAN_FilterInitStructure.CAN_FilterFIFOAssignment=CAN_FIFO0;// 设定了指向过滤器的FIFO为0
	CAN_FilterInitStructure.CAN_FilterActivation=ENABLE;// 使能过滤器
	CAN_FilterInit(&CAN_FilterInitStructure);//	按上面的参数初始化过滤器

	/* CAN FIFO0 message pending interrupt enable */ 
	CAN_ITConfig(CAN1,CAN_IT_FMP0, ENABLE); //使能FIFO0消息挂号中断
 }  

Two, CAN bus communication-baud rate calculation

1. CAN bus time characteristics

• Synchronization segment (SYNC_SEG) : It is usually expected that the bit change occurs in this time period. Its value is fixed at 1 time unit (1 x tCAN).
• Time period 1 (BS1) : Define the location of the sampling point. It includes PROP_SEG and PHASE_SEG1 in the CAN standard. Its value can be programmed from 1 to 16 time units, but it can also be automatically extended to compensate for the positive shift in phase caused by the frequency difference of different nodes in the network.
• Time period 2 (BS2) : Define the location of the sending point. It represents PHASE_SEG2 in the CAN standard. Its value can be programmed from 1 to 8 time units, but it can also be automatically shortened to compensate for negative phase shifts.
  

2. Baud rate calculation formula

CAN baud rate = APB bus frequency/BRP divider/(1+tBS1+tBS2)

3. Registers related to CAN baud rate

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