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。