4.CAN接收初始化

void init_msg_object_RX (char MsgNum,uchar id) { uint temp; SFRPAGE = CAN0_PAGE; CAN0ADR = IF2CMDMSK; CAN0DAT = 0x00fb; /* IF2 Command Mask Registers =0x00fb WR/RD=1,Mask=1,Arb=1,Control=1,ClrIntPnd=1,TxRqst=0,DataA=1,DataB=1,一次接收8字節數據*/ CAN0ADR = IF2MSK1; CAN0DAT = 0x0000; CAN0DAT = 0x0000; CAN0ADR = IF2ARB1; CAN0DAT = 0x0000; /*IF2 Arbitration Registers1 =0x0000，即ID15-0=0*/ temp=id<<2;//標準id為ID28-ID18,所以要左移2位 temp&=0x1fff; temp|=0x8000; CAN0DAT = temp; /*IF2 Arbitration Registers2=100(id)00b MsgVal=1,Xtd=0,為標準模式，擴展ID無效，Dir=0，為接收*/ CAN0DAT = 0x0488; /*IF2 Message Control Registers=0x0488 NewDat=0,MsgLst=0,IntPnd=0,UMask=0,TxIE=0,RxIE=1,接收中斷使能;RmtEn=0,TxRqst=0 EoB=1,DLC3-0=1000,即數據長度為8*/ CAN0ADR = IF2CMDRQST; CAN0DATL = MsgNum; /*IF2 Command Request Registers=MsgNum,將以上配置寫入MsgNum號消息*/ }

5.CAN波特率設置
Calculation of the CAN bit timing :

System clock f_sys = 22.1184 MHz/2 = 11.0592 MHz.
System clock period t_sys = 1/f_sys = 90.422454 ns.
CAN time quantum tq = t_sys (at BRP = 0)

Desired bit rate is 1 MBit/s, desired bit time is 1000 ns.
Actual bit time = 11 tq = 996.65ns ~ 1000 ns
Actual bit rate is 1.005381818 MBit/s = Desired bit rate+0.5381%

CAN bus length = 10 m, with 5 ns/m signal delay time.
Propagation delay time : 2*(transceiver loop delay + bus line delay) = 400 ns
(maximum loop delay between CAN nodes)

Prop_Seg = 5 tq = 452 ns ( >= 400 ns).
Sync_Seg = 1 tq

Phase_seg1 + Phase_Seg2 = (11-6) tq = 5 tq
Phase_seg1 <= Phase_Seg2, => Phase_seg1 = 2 tq and Phase_Seg2 = 3 tq
SJW = (min(Phase_Seg1, 4) tq = 2 tq

TSEG1 = (Prop_Seg + Phase_Seg1 - 1) = 6
TSEG2 = (Phase_Seg2 - 1) = 2
SJW_p = (SJW - 1) = 1

Bit Timing Register = BRP + SJW_p*0x0040 = TSEG1*0x0100 + TSEG2*0x1000 = 2640

Clock tolerance df :

A: df < min(Phase_Seg1, Phase_Seg2) / (2 * (13*bit_time - Phase_Seg2))
B: df < SJW / (20 * bit_time)

A: df < 2/(2*(13*11-3)) = 1/(141-3) = 1/138 = 0.7246%
B: df < 2/(20*11) = 1/110 = 0.9091%

Actual clock tolerance is 0.7246% - 0.5381% = 0.1865% (no problem for quartz)

SFRPAGE = CAN0_PAGE; CAN0CN=0X41; CAN0ADR=BITREG; CAN0DAT=0x2640;//調波特率

6.發送函數

void transmit (char MsgNum) { uchar num; SFRPAGE = CAN0_PAGE; CAN0ADR = IF1CMDMSK; CAN0DAT = 0x0087; /* IF1 Command Mask Registers =0x0087 WR/RD=1,Mask=0,Arb=0,Control=0,ClrIntPnd=0,TxRqst=1,DataA=1,DataB=1,一次發送8字節數據*/ CAN0ADR = IF1DATA1; /*將8字節數據寫入IF1*/ for(num=0;num<4;num++) { CAN0DATH=sdata[2*num+1]; CAN0DATL=sdata[2*num]; } CAN0ADR = IF1CMDRQST; CAN0DATL = MsgNum; //將以上配置寫入MsgNum號CAN消息 }

7.接收函數

void receive_data (uchar MsgNum) { uchar i; SFRPAGE = CAN0_PAGE; CAN0ADR = IF2CMDMSK; CAN0DATL = 0x0f; /* IF1 Command Mask Registers =0xxx0f WR/RD=0,Mask=0,Arb=0,Control=0,ClrIntPnd=1,NewDat=1,DataA=1,DataB=1,一次發送8字節數據*/ CAN0ADR = IF2CMDRQST; CAN0DATL = MsgNum; //指向MsgNum號消息 CAN0ADR = IF2DATA1; for(i=0;i<4;i++) rdata[i].tempval=CAN0DAT;//接收數據 isnewdata=1; }

　　最后現象：單片機發送成功，PC端能成功接收發送的數據。而單片機接收CAN總線數據時異常。TJA1050芯片的RXD引腳能檢測到電壓變化，而單片機Status Register寄存器中RxOk位為‘1’，但沒有產生接收中斷，接收消息對象中的數據也未改變。

　　其中0x02為發送消息對象，0x04為接收消息對象。

　　CAN0STA為Status Register寄存器中低8位。RxOk為‘1’。
　　將單片機設置為測試模式，CAN Control Register寄存器中Test位置1。使用回路靜音模式時，將CAN Test Register寄存器LBack和Silent同時置1，使TX與RX自身形成回路，單片機自發自收。結果為單片機接收不到自己發送的數據。

　　使用測試模式中的基本模式時，將CAN Test Register寄存器Basic位置1。此模式下，控制器不使用消息內存，即控制器不使用32個消息對象，而是將IF1寄存器作為發送緩存區，將IF2寄存器作為接收緩存區。此模式下，單片機發送數據正常，接收數據時，IF2寄存器緩存區接收到的數據不正確。
　　最終，通信失敗原因尚未得知。。。