STM32F107 CAN滤波器设置解析

该部分程序如下：

  CAN_FilterInitStructure.CAN_FilterNumber=14;  //选择滤波器组，共14个
  CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask; //过滤模式，选择位屏蔽模式而不是标识符列表模式
  CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;//1个32位寄存器
  CAN_FilterInitStructure.CAN_FilterIdHigh=(((u32)0x4321<<3)&0xFFFF0000)>>16;//要过滤的ID高位
  CAN_FilterInitStructure.CAN_FilterIdLow=(((u32)0x4321<<3)|CAN_ID_EXT|CAN_RTR_DATA)&0xFFFF;要过滤的ID低位
  CAN_FilterInitStructure.CAN_FilterMaskIdHigh=0xffff;//0x0000;//收到的ID每一位必须与必须滤波寄存器中的每一位相等
  CAN_FilterInitStructure.CAN_FilterMaskIdLow=0xffff;//0x0000;
  CAN_FilterInitStructure.CAN_FilterFIFOAssignment=CAN_FIFO0;
  CAN_FilterInitStructure.CAN_FilterActivation=ENABLE;
  CAN_FilterInit(&CAN_FilterInitStructure);  
   /* transmit */
  //TxMessage.StdId=0x12;
  TxMessage.ExtId=0x1234;
  //TxMessage.IDE=CAN_ID_EXT;
  TxMessage.IDE=CAN_ID_EXT;//CAN_ID_STD;
  TxMessage.RTR=CAN_RTR_DATA;
  TxMessage.DLC = 2;
  TxMessage.Data[0]='N';
  TxMessage.Data[1]='2';
  CAN_ITConfig(CAN2, CAN_IT_FMP0, ENABLE);
  //TxMessage.Data[0] ='h';
  CAN_Transmit(CAN2, &TxMessage);

CAN_FilterIdHigh 和CAN_FilterIdLow为什么这么设置呢，看看下图就明白了。

以上是扩展帧，对于标准帧怎么处理呢

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