大家好,我现在急需要大家的帮助,在调试XDP512的过程中,遇到了一个很奇怪的问题.

要求总线速率是250kps,我用的晶振是无源12MHZ的晶体,在BDM调试时,其上的AD,IO等功能均调试

成功,但在总线调试时却遇到了一个大问题.为实现250kps的速率,即位时间为4us,我选用4分频,同步跳转宽

度为1TQ,时间段1为6TQ,时间段2为5TQ,选用外部晶振.标准帧,发送0x55数据,但却不成功.总线分析仪却检

测不到任何信息,总线负载显示为 86%,用示波器检测发现总线波形是对的,所发送的数据无误.但位时间却

19us左右,这是为什么呢?请大家帮帮忙.项目要交了,压力太大了.

我分析可能是:1.是否是因为在BDM调试状态下,造成非实时呢?

2. 波特率设得不对,但检查无误啊

3. 外置晶振偏差太大,这可从来未遇到过,还有如果是晶振的问题,如何检测呢?

谢谢

CANCTL1 &= 0xbf;

（须在CAN初始化状态下执行）

[此贴子已经被作者于2009-5-30 10:10:29编辑过]

应该可以了。

[此贴子已经被作者于2009-5-30 10:04:51编辑过]

感谢fish1330的观注.

以下是我的程序:

/* Acceptance Code Definitions */

#define ACC_CODE_ID100 0x2000

#define ACC_CODE_ID100_HIGH ((ACC_CODE_ID100&0xFF00)>>8)

#define ACC_CODE_ID100_LOW (ACC_CODE_ID100&0x00FF)

/*switch information*/

#define Switch_ID111 0x111

#define Switch_ID111_HIGH ((Switch_ID111&0xFF00)>>8)

#define Switch_ID111_LOW (Switch_ID111&0x00FF)

/*Check information*/

#define Check_ID241 0x241

#define Check_ID241_HIGH ((Check_ID241&0xFF00)>>8)

#define Check_ID241_LOW (Check_ID241&0x00FF)

/*Velocity information*/

#define Velocity_ID421 0x421

#define Velocity_ID421_HIGH ((Velocity_ID421&0xFF00)>>8)

#define Velocity_ID421_LOW (Velocity_ID421&0x00FF)

/*Temperature information*/

#define Temperature_ID451 0x451

#define Temperature_ID451_HIGH ((Temperature_ID451&0xFF00)>>8)

#define Temperature_ID451_LOW (Temperature_ID451&0x00FF)

/*CAN0初始化函数*/

void CAN0Initial(void) {

CAN0CTL0 = 0x01; /* Enter Initialization Mode,请求进入初始化模式

* CAN0CTL0 CAN0控制寄存器0,用以请求进入初始化模式

* 0b00000001

* ||||||||__ INITRQ(Enter Initialization Mode)初始化请求位

* |||||||___ SLPRQ(Sleep Mode Request bit)休眠模式请求位

* ||||||____ WUPE(Wake-Up disabled)唤醒允许位

* |||||_____ TIME(Time stamping disabled)定时器允许位

* ||||______ SYNCH(Synchronized Status)同步状态位

* |||_______ CSWAI(CAN not affected by Wait)等待模式下CAN停止控制位

* ||________ RXACT(Receiver Active Status bit)接收数据指示位

* |_________ RXFRM(Received Frame Flag bit)接收帧标志位

*/

while (CAN0CTL1_INITAK==0){};/* Wait for Initialization Mode acknowledge

* INITRQ bit = 1时,表示已进入初始化模式

*/

CAN0CTL1 = 0x80; /* Enable MSCAN module and LoopBack Mode,使能CAN,选择外部时钟,

* CAN0CTL1 CAN0控制寄存器0

* 0b10000000

* ||||||||__ INITAK(Initialization Mode Acknowledge)初始化确认位

* |||||||___ SLPAK(Sleep Mode Acknowledge)休眠模式确认位

* ||||||____ WUPM(Wake-up low-pass filter disabled)

* |||||_____ BORM(Bus-Off Recovery Mode)下线恢复模式控制位

* ||||______ LISTEN(Listen Only Mode disabled)

* |||_______ LOOPB(Loop Back Mode enabled)监控自检模式控制位

* ||________ CLKSRC(Ext Osc/Xtal as Clock Source)时钟源选择位

* |_________ CANE(MSCAN Module enabled)使能CAN总线控制位

*/

CAN0BTR0 = 0x03; /* Synch Jump = 1 Tq clock Cycles,预分频为4

* MSCAN Bus Timing Register 0,总线定时寄存器0

* 0b00000011

* ||||||||__BRP0=1

* |||||||___BRP1=1

* ||||||____BRP2=0

* |||||_____RPP3=0

* ||||______BRP4=0

* |||_______BRP5=0,即预分频为4

* ||________SJW0=0

* |_________SJW1=0,即同步跳转宽度为1Tq

*/

CAN0BTR1 = 0x45; /* Set Number of samples per bit, TSEG1 and TSEG2,设置1和2时间段

* MSCAN Bus Timing Register 1, 总线定时寄存器1

* 0b01000101

* ||||||||__TSEG10=1

* |||||||___TSEG11=0

* ||||||____TSEG12=1

* |||||_____TSEG13=0,即时间段1为6 Tq

* ||||______TSEG20=0

* |||_______TSEG21=0

* ||________TSEG22=1,时间段2宽度为5 Tq

* |_________SAMP=0, 即每位进行1次采样,1时每位进行3次采样

*/

CAN0IDAC = 0x10; /* Set four 16-bit Filters,设置接收控制寄存器,

* MSCAN Identifier Acceptance Control Register

* 0b00010000

* ||||||||__IDHIT0

* |||||||___IDHIT1

* ||||||____IDHIT2,滤波器应用指示位

* |||||_____ Unimplemented

* ||||______IDAM0=1

* |||_______IDAM1=0,即4个16位接收滤波器

* ||________

* |_________>- Unimplemented

*/

/* Acceptance Filters */

CAN0IDAR0 = Switch_ID111_HIGH; //|\ 16 bit Filter 0

CAN0IDMR0 = 0x00; //| \__ Accepts Standard Data Frame Msg

CAN0IDAR1 = Switch_ID111_LOW; //| / with ID 0x111

CAN0IDMR1 = 0x00; //|/

CAN0IDAR2 = Check_ID241_HIGH; //|\ 16 bit Filter 1

CAN0IDMR2 = 0x00; //| \__ Accepts Standard Data Frame Msg

CAN0IDAR3 = Check_ID241_LOW; //| / with ID 0x241

CAN0IDMR3 = 0x00; //|/

CAN0IDAR4 = Velocity_ID421_HIGH; //|\ 16 bit Filter 2

CAN0IDMR4 = 0x00; //| \__ Accepts Standard Data Frame Msg

CAN0IDAR5 = Velocity_ID421_LOW; //| / with ID 0x421

CAN0IDMR5 = 0x00; //|/

CAN0IDAR6 = Temperature_ID451_HIGH; //|\ 16 bit Filter 3

CAN0IDMR6 = 0x00; //| \__ Accepts Standard Data Frame Msg

CAN0IDAR7 = Temperature_ID451_LOW; //| / with ID 0x451

CAN0IDMR7 = 0x00; //|/

CAN0CTL0 = 0x00; /* Exit Initialization Mode Request */

while (CAN0CTL1_INITAK==1){}; /* Wait for Normal Mode */

CAN0RIER_RXFIE=1; /*允许CAN0的接收中断*/

}

fish1330所提:

"在初始化函数的最后增加这句话：

CANCTL1 &= 0xbf;

（须在CAN初始化状态下执行）"

是要求选择外部晶振时钟,可我已在初始化程序中置

CAN0CTL1 = 0x80;使能CAN,选择外部晶振时钟了,难道一定要在初始化函数最后一句吗?请教.

发送函数应无问题,因为的发送的数据用示波器能检测到,是正确的.关键问题是位速率不对.让我很奇怪.因为以前没用过此类单片机.不知在BDM调试下与脱机运行是否不同.在PIC单片机的调试状态下,总线发送都很正常.请大家帮我查一下为什么位时间不对的原因.谢谢!

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