基于stm32的can总线彻底研究

1、CAN总线的初始化

void can_init(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;//禁止时间触发通信模式
      CAN_InitStructure.CAN_ABOM=DISABLE;
      CAN_InitStructure.CAN_AWUM=DISABLE;
      CAN_InitStructure.CAN_NART=DISABLE;//CAN报文只被发送1次，不管发送的结果如何（成功、出错或仲裁丢失） 
      CAN_InitStructure.CAN_RFLM=DISABLE;
      CAN_InitStructure.CAN_TXFP=DISABLE;
      CAN_InitStructure.CAN_Mode=CAN_Mode_Normal;
      //CAN_Mode_LoopBack
      //CAN_Mode_Normal
      CAN_InitStructure.CAN_SJW=CAN_SJW_1tq;
      CAN_InitStructure.CAN_BS1=CAN_BS1_5tq;//1--16
      CAN_InitStructure.CAN_BS2=CAN_BS2_2tq;//1--8
      CAN_InitStructure.CAN_Prescaler=2;
      CAN_Init(&CAN_InitStructure);
#ifdef can_id_filter
       /* CAN filter init */
      CAN_FilterInitStructure.CAN_FilterNumber=0;//选择过滤器0
      CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask;//指定过滤器被设置为标识符屏蔽模式
      CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;//给出过滤器位宽为32位
      CAN_FilterInitStructure.CAN_FilterIdHigh=slave_id<<5;//过滤器标识符
      CAN_FilterInitStructure.CAN_FilterIdLow=0x0000;//
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh=0xffff;//过滤器屏蔽标识符
      CAN_FilterInitStructure.CAN_FilterMaskIdLow=0xfffc;
      CAN_FilterInitStructure.CAN_FilterFIFOAssignment=0;//选择FIFO0
      CAN_FilterInitStructure.CAN_FilterActivation=ENABLE;//使能过滤器
      CAN_FilterInit(&CAN_FilterInitStructure);//进入初始化函数
#else
      /* CAN filter init */
      CAN_FilterInitStructure.CAN_FilterNumber=0;//选择过滤器0
      CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask;//指定过滤器被设置为标识符屏蔽模式
      CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;//给出过滤器位宽为32位
      CAN_FilterInitStructure.CAN_FilterIdHigh=0x0000;//过滤器标识符
      CAN_FilterInitStructure.CAN_FilterIdLow=0x0000;//
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh=0x0000;//过滤器屏蔽标识符
      CAN_FilterInitStructure.CAN_FilterMaskIdLow=0x0000;
      CAN_ITConfig(CAN_IT_FMP0, ENABLE);//使能指定的can中断
}

 

 

void CAN_DeInit(void)
{
  /* Enable CAN reset state */
  RCC_APB1PeriphResetCmd(RCC_APB1Periph_CAN, ENABLE);
  /* Release CAN from reset state */
  RCC_APB1PeriphResetCmd(RCC_APB1Periph_CAN, DISABLE);
}

2、发送程序

unsigned char CAN_PushMessage(CAN_MSG  *pTransmitBuf )
{
  u8 TransmitMailbox=0;
  CanTxMsg TxMessage;
  if(pTransmitBuf -> LEN > 8)
  {
       return  1;
  }
  /* transmit */
  TxMessage.StdId=pTransmitBuf ->StdId;//用来设定标准标识符（0-0x7ff，11位）
  TxMessage.ExtId=pTransmitBuf ->ExtId;
  TxMessage.RTR=  pTransmitBuf ->RTR;//设置RTR位为数据帧
  TxMessage.IDE=  pTransmitBuf ->IDE;//标识符扩展位，为标准帧
  TxMessage.DLC=  pTransmitBuf ->LEN;//设置数据长度
  //根据DLC字段的值，将有效数据拷贝到发送数据寄存器
  memcpy(TxMessage.Data, pTransmitBuf ->BUF,pTransmitBuf ->LEN);
  TransmitMailbox = CAN_Transmit(&TxMessage);
 // TxMessage.Data[1]=(data & 0xff00)>>8;
  return 1;
}

3、中断接收程序

void USB_LP_CAN_RX0_IRQHandler(void)
{
  //清空can接收缓存
  CanRxMsg RxMessage;
  RxMessage.StdId=0x00;
  RxMessage.ExtId=0x00;
  RxMessage.IDE=0;
  RxMessage.DLC=0;
  RxMessage.FMI=0;//CAN过滤主控制寄存器
  memset( &RxMessage.Data[0],0,8);
  //can总线接收数据函数
  CAN_Receive(CAN_FIFO0, &RxMessage);
  //将接收到的数据写于modbus的寄存器1
  //modbus_regester[1]=(RxMessage.Data[0]<<8)|(RxMessage.Data[1]);
 // if((RxMessage.StdId==slave_id) && (RxMessage.ExtId==0x00) && (RxMessage.IDE==CAN_ID_STD))
  {
    //将can接收标志位置1，表示从卡应经接收到一个can报文
    flag_can_recv=0;
    memcpy(can_rx_data,&RxMessage.Data,RxMessage.DLC);
      flag_can_recv=1;
  }

}

4、can总线的id过滤

对扩展数据帧过滤：

CAN_FilterInitStructure.CAN_FilterNumber   = 0; 
CAN_FilterInitStructure.CAN_FilterMode     = CAN_FilterMode_IdMask; 
CAN_FilterInitStructure.CAN_FilterScale    = CAN_FilterScale_32bit; 
CAN_FilterInitStructure.CAN_FilterIdHigh = (((u32)CAN_ID<<3)&0xFFFF0000)>>16; 
CAN_FilterInitStructure.CAN_FilterIdLow= (((u32)CAN_ID<<3)|CAN_ID_EXT|CAN_RTR_DATA)&0xFFFF; 
CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF; 
CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFF; 

对标准数据帧过滤：

CAN_FilterInitStructure.CAN_FilterIdHigh= (((u32)CAN_ID0<<21)&0xFFFF0000)>>16; 
CAN_FilterInitStructure.CAN_FilterIdLow=(((u32)CAN_ID0<<21)|CAN_ID_STD|CAN_RTR_DATA)&0xFFFF; 
CAN_FilterInitStructure.CAN_FilterMaskIdHigh   = 0xFFFF; 
CAN_FilterInitStructure.CAN_FilterMaskIdLow    = 0xFFFF;

假如要对标准远程帧进行过滤,那么：

只需要将

CAN_FilterInitStructure.CAN_FilterIdLow=(((u32)CAN_ID0<<21)|CAN_ID_STD|CAN_RTR_DATA)&0xFFFF; 改成：

CAN_FilterInitStructure.CAN_FilterIdLow=(((u32)CAN_ID0<<21)|CAN_ID_STD|CAN_RTR_REMOTE)&0xFFFF;

5、can总线的帧格式

数据帧格式：

远程帧格式：

6、can总线的逻辑电平

can总线的物理连接有两根线：CANH和CANL，以差分的形式输出。

（有的时候有地线，作为屏蔽线使用）

can总线的高电平 3.5v，表示逻辑0

can总线的低电平 1.5v，表示逻辑1

7、CAN总线的波特率计算

can时钟是RCC_APB1PeriphClock，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 

8、can总线的仲裁机制

根据仲裁来判断优先级：

(1) 若在同一时刻，标准格式的报文与扩展格式的报文同时抢占总线，且它们的基础ID相同，则发标准格式的报文节点就会PK成功。这是因为扩展格式在基本ID后，紧接着是SRR位，与IDE位，且这两位都是隐性位。而在标准格式中，这两位分别对应的位为RTR与r1，其中RTR既可以为隐性位，也可以为显性位，，但是r1必须为显性位。由仲裁规则可以此时标准帧必定胜出。

(2)  同理，如果在同一时刻，具有相同格式，且具有相同ID的数据帧与远程帧争夺总线控制权，那么数据帧必定胜出。因为RTR显性表示数据帧，隐性表示远程帧。

stm32的can总线的配置如下：

      CAN_InitStructure.CAN_TTCM=DISABLE;//禁止时间触发通信模式
      CAN_InitStructure.CAN_ABOM=DISABLE;
      CAN_InitStructure.CAN_AWUM=DISABLE;
      CAN_InitStructure.CAN_NART=DISABLE;//CAN报文只被发送1次，不管发送的结果如何（成功、出错或仲裁丢失） 
      CAN_InitStructure.CAN_RFLM=DISABLE;
      CAN_InitStructure.CAN_TXFP=DISABLE;
      CAN_InitStructure.CAN_Mode=CAN_Mode_Normal;
      //CAN_Mode_LoopBack
      //CAN_Mode_Normal
      CAN_InitStructure.CAN_SJW=CAN_SJW_1tq;
      CAN_InitStructure.CAN_BS1=CAN_BS1_5tq;//1--16
      CAN_InitStructure.CAN_BS2=CAN_BS2_2tq;//1--8
      CAN_InitStructure.CAN_Prescaler=2;

      CAN_Init(&CAN_InitStructure);

       /* CAN filter init */
      CAN_FilterInitStructure.CAN_FilterNumber=0;//选择过滤器0
      CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask;//指定过滤器被设置为标识符屏蔽模式
      CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;//给出过滤器位宽为32位

 

下面根据设置的参数不同来决定can总线can总线的配置情况：

1、对扩展数据帧进行过滤:(只接收扩展数据帧)
      CAN_FilterInitStructure.CAN_FilterIdHigh   = (((u32)slave_id<<3)&0xFFFF0000)>>16;
      CAN_FilterInitStructure.CAN_FilterIdLow   = (((u32)slave_id<<3)|CAN_ID_EXT|CAN_RTR_DATA)&0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFF;
(注：标准帧数据帧、标准远程帧和扩展远程帧均被过滤)
2、对扩展远程帧过滤:(只接收扩展远程帧)
      CAN_FilterInitStructure.CAN_FilterIdHigh   = (((u32)slave_id<<3)&0xFFFF0000)>>16;
      CAN_FilterInitStructure.CAN_FilterIdLow   = (((u32)slave_id<<3)|CAN_ID_EXT|CAN_RTR_REMOTE)&0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFF;

3、对标准远程帧过滤:(只接收标准远程帧)
      CAN_FilterInitStructure.CAN_FilterIdHigh   = (((u32)slave_id<<21)&0xffff0000)>>16;
      CAN_FilterInitStructure.CAN_FilterIdLow   = (((u32)slave_id<<21)|CAN_ID_STD|CAN_RTR_REMOTE)&0xffff;
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFF;
4、对标准数据帧过滤:(只接收标准数据帧)
      CAN_FilterInitStructure.CAN_FilterIdHigh   = (((u32)slave_id<<21)&0xffff0000)>>16;
      CAN_FilterInitStructure.CAN_FilterIdLow   = (((u32)slave_id<<21)|CAN_ID_STD|CAN_RTR_DATA)&0xffff;
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFF;

5、对扩展帧进行过滤:(扩展帧不会被过滤掉)
      CAN_FilterInitStructure.CAN_FilterIdHigh   = (((u32)slave_id<<3)&0xFFFF0000)>>16;
      CAN_FilterInitStructure.CAN_FilterIdLow   = (((u32)slave_id<<3)|CAN_ID_EXT)&0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFC;
6、对标准帧进行过滤:(标准帧不会被过滤掉)
      CAN_FilterInitStructure.CAN_FilterIdHigh   = (((u32)slave_id<<21)&0xffff0000)>>16;
      CAN_FilterInitStructure.CAN_FilterIdLow   = (((u32)slave_id<<21)|CAN_ID_STD)&0xffff;
      CAN_FilterInitStructure.CAN_FilterMaskIdHigh  = 0xFFFF;
      CAN_FilterInitStructure.CAN_FilterMaskIdLow   = 0xFFFC;
注：slave_id为要过滤的id号。