CAN 總線在控制領(lǐng)域使用的非常廣泛，如今大多數(shù)CPU芯片外圍都擴(kuò)展CAN接口。本文重點介紹以STM32F103E系列芯片為基礎(chǔ)介紹CAN 總線的使用方法。

1. 硬件基礎(chǔ)

CAN總線工作需要兩根數(shù)據(jù)線，RX和TX，即為輸入總線和輸出總線。一般CPU與外界通信需要接一個驅(qū)動芯片（這點很像UART接口），常用的CAN芯片主要有：SN65VHD230、PCA82C250T等，本系統(tǒng)使用SN65VHD230作為CAN接口芯片。而CPU提供的CAN接口為CAN_L和CAN_H。

2. 軟件設(shè)計

在進(jìn)行軟件設(shè)計時，我們首先來看這樣的一個結(jié)構(gòu)體：

typedef struct
{
uint32_t StdId;

uint32_t ExtId;

uint8_t IDE;

uint8_t RTR;

uint8_t DLC;

uint8_t Data[8];
} CanTxMsg;

這是定義一個can數(shù)據(jù)包的結(jié)構(gòu)體，即一個CAN數(shù)據(jù)包包含以上幾個部分。

現(xiàn)在我們思考一個問題：由于can可連接多個節(jié)點，如果一個系統(tǒng)為星形網(wǎng)絡(luò)連接方式，那么主機(jī)應(yīng)該怎樣區(qū)別這些從機(jī)發(fā)送的信息呢？

答案在上面那個結(jié)構(gòu)體中，我們可以給每個分機(jī)定義一個ID，那么主機(jī)在接收到分機(jī)發(fā)送的數(shù)據(jù)后，通過ID號判別接收到的信息是那個從機(jī)發(fā)送的。

注意： DLC定義發(fā)送數(shù)據(jù)的長度，其范圍為：0~8。

下面我們來編寫CAN驅(qū)動：



對CAN模塊初始化

void CAN_CfgInit(void)
{
CAN_InitTypeDefCAN_InitStructure;
CAN_FilterInitTypeDefCAN_FilterInitStructure;

CAN_PortInit();
CAN_DeInit(CAN1);
CAN_StructInit(&CAN_InitStructure);

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(CAN1, &CAN_InitStructure);

CAN_FilterInitStructure.CAN_FilterNumber=0;
CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask;
CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;
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_FilterFIFOAssignment=CAN_FIFO0;
CAN_FilterInitStructure.CAN_FilterActivation=ENABLE;
CAN_FilterInit(&CAN_FilterInitStructure);

CAN_ITConfig(CAN1, CAN_IT_FMP0, ENABLE);
}

這里為can 定義一個專門的結(jié)構(gòu)體，便于數(shù)據(jù)處理：

typedef struct CAN_Socket CAN;
struct CAN_Socket {
INT32U u32_StdId;
INT32U u32_ExtId;
INT8Uu8_IDE;
INT8Uu8_RTR;
INT8Uu8_DLC;
INT8Uu8_FMI;
INT8Uu8_data[8];
};

數(shù)據(jù)打包，并且發(fā)送

void CAN_TxSocket( CAN *can_Socket )
{
INT8U i = 0;
CanTxMsg TxMessage;

CAN_ITConfig(CAN1, CAN_IT_FMP0, ENABLE);// CAN FIFO0 message pending interrupt enable
// Transmit a message
TxMessage.StdId=can_Socket->u32_StdId;
TxMessage.ExtId=can_Socket->u32_ExtId;
TxMessage.IDE=can_Socket->u8_IDE;
TxMessage.RTR= can_Socket->u8_RTR;
TxMessage.DLC=can_Socket->u8_DLC;
for( i =0; i
TxMessage.Data= can_Socket->u8_data;
}
CAN_Transmit(CAN1, &TxMessage);
CAN_ITConfig(CAN1, CAN_IT_FMP0, DISABLE);// Disable interrupt handling
}



接收函數(shù)放在中斷程序中處理：



void USB_LP_CAN1_RX0_IRQHandler(void)
{
CanRxMsg RxMessage;
INT8U i = 0;
INT8U u8_RxLen = 0;

RxMessage.StdId = 0x00;
RxMessage.ExtId = 0x00;
RxMessage.IDE = 0;
RxMessage.RTR = 0;
RxMessage.DLC = 0;
RxMessage.FMI = 0;
for( i=0;i<8;i++){
RxMessage.Data=0x00;
}

CAN_Receive(CAN1, CAN_FIFO0, &RxMessage);
u8_RxLen = RxMessage.DLC;
if((RxMessage.ExtId==0x12) && (RxMessage.IDE==CAN_ID_EXT)){
for( i=0;i
CAN_ReceiveBuff= RxMessage.Data;
}
}
}



這里只介紹CAN使用方法和主要驅(qū)動程序，測試程序可自行設(shè)計。

本人的測試程序：

~INT8U SendBuff1[]="Hello";
INT8U SendBuff2[]="World";
INT8U SendBuff3[]="ADC= 255";
void main(void)
{
System_HardwareInit();
while (1)
{
CAN_Tx(SendBuff1);
Disp_CanReceveData();
CAN_Tx(SendBuff2);
Disp_CanReceveData();
CAN_Tx(SendBuff3);
Disp_CanReceveData();
}
}



接收數(shù)據(jù)，并在液晶上打印出來！

void Disp_CanReceveData( void )
{
INT8U u8_CanRecBuff[64];

if(CAN_ReceiveBuff[0] == H){
sprintf(( char *)u8_CanRecBuff,"CAN receve buff1 is : %s",CAN_ReceiveBuff);
GCLDASC_PutChar16x16Str(10,30,u8_CanRecBuff, Red, Green, 1);
}
if(CAN_ReceiveBuff[0] == W){
sprintf(( char *)u8_CanRecBuff,"CAN receve buff2 is : %s",CAN_ReceiveBuff);
GCLDASC_PutChar16x16Str(10,50,u8_CanRecBuff, Red, Green, 1);
}
if(CAN_ReceiveBuff[0] == A){
sprintf(( char *)u8_CanRecBuff,"CAN receve buff3 is : %s",CAN_ReceiveBuff);
GCLDASC_PutChar16x16Str(10,70,u8_CanRecBuff, Red, Green, 1);
}
}