use the MC912ZVC with 16MHZ and CAN 250kb

[thorstenmulun]

Hello,

can some one help me? I find only exampels with 4MHZ Quarz with 250kb and i dont understand what i have to change in the Configbits to use a 16MHZ Quarz and 250kb

//initialises CAN communications

void CAN_init(void){

//initialise MSCAN

CAN0CTL0 = 0x01;

while (!(CAN0CTL1_INITAK)){}

CAN0CTL1_CANE = 1; /* Enable MSCAN module */

CAN0CTL1_CLKSRC = 0; /* Clock source is OSCCLK = 20 MHz */

CAN0CTL1_LOOPB = 0; /* Set to 1 for LoopBack Mode, 0 otherwise */

CAN0CTL1_LISTEN = 0; /* Not listen only mode */

CAN0CTL0_WUPE = 1; /* Enable WAKEUP */

//Baud rate = CANCLK/(Pre-scaler * time quanta)

CAN0BTR1_TSEG_10 = 0x0A; // that works with 4MHZ

CAN0BTR1_TSEG_20 = 0x03; // and 250kb

CAN0BTR0_BRP = 0x00; //

CAN0BTR0_SJW = 0x03;

CAN0BTR1_SAMP = 0;

Can some one tell me the right value?

Thanks a lot

Thorsten

[RadekS]

Hi Thorsten,

Please look at attached CAN baudrate calculator.

Enter your oscillator clock, required CAN speed and Physical Interface Tx+ Rx propagation delay.

Calculator will highlight CANBTR0 and CANBTR1 register values. For example:

16MHz, 250bit/s, 255ns -> CANBTR0 = 0xC3, CANBTR1 = 0x67.

So, you could replace code

CAN0BTR1_TSEG_10 = 0x0A; // that works with 4MHZ

CAN0BTR1_TSEG_20 = 0x03; // and 250kb

CAN0BTR0_BRP = 0x00; //

CAN0BTR0_SJW = 0x03;

CAN0BTR1_SAMP = 0;

By these lines:

CANBTR0 = 0xC3;

CANBTR1 = 0x67;

I hope it helps you.

Have a great day,
RadekS

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[thorstenmulun]

Hi RadekS,

sorry but it dosent works:(

I think i have a Problem witch the PLL settings but wich?

Here my complet Config

//initialises the PLL

void PLL_init(void){

    CPMUCLKS_PLLSEL = 1;                //FBUS = FPLL/2.   FBUS = 32MHz,

    CPMUREFDIV_REFFRQ = 3;                //                 Reference clock > 12MHz   

    CPMUREFDIV_REFDIV = 0x3;            //FREF=8/(1+1) = 4MHZ       

    CPMUSYNR_VCOFRQ = 0x1;                 //FVCO is between 48MHZ and 80MHZ   

    CPMUSYNR_SYNDIV = 0x1;                //FVCO = 2xFREFx(SYNDIV+1)   =   FVCO = 2x4x(7+1) = 64MHZ

    CPMUPOSTDIV_POSTDIV = 0x0;            //FPLL = FVCO/(POSTDIV+1).  FPLL = 64MHZ/(0+1)    FPLL = 64MHz   

    CPMUOSC_OSCE = 1;                    //External oscillator enable. 8MHZ.        FREF=FOSC/(REFDIV+1)       

    while(!CPMUIFLG_LOCK){}                // Wait for LOCK.         

    CPMUIFLG = 0xFF;                    // clear CMPMU int flags - not needed but good practice   

}

//initialises CAN communications

void CAN_init(void){

    //initialise MSCAN

    CAN0CTL0 = 0x01;

    while (!(CAN0CTL1_INITAK)){}

    //initialise MSCAN

        CAN0CTL0 = 0x01;

        while (!(CAN0CTL1_INITAK)){}

        CAN0CTL1_CANE = 1;      /* Enable MSCAN module */

        CAN0CTL1_CLKSRC = 0;    /* Clock source is OSCCLK = 16 MHz */   

        CAN0CTL1_LOOPB = 0;     /* Set to 1 for LoopBack Mode, 0 otherwise */

        CAN0CTL1_LISTEN = 0;    /* Not listen only mode */ 

        CAN0CTL0_WUPE = 1;        /* Enable WAKEUP */

        CAN0BTR0 = 0xC3;

        CAN0BTR1 = 0x67;       

in the PLL Area i try some different values,i think thats my problem but i dont anderstand the exampel.me english is not so good 

thanks for your help    

[RadekS · Accepted solution]

Hi Thorsten,

You are right, your PLL setting is not correct.

I would like to recommend (for 32MHz bus clock from 16MHz crystal):

CPMUREFDIV_REFFRQ = 0x3;                //Reference clock > 12MHz

CPMUREFDIV_REFDIV = 0x0;            //FREF=16/(0+1) = 16MHZ    

CPMUSYNR_VCOFRQ = 0x1;                //FVCO is between 48MHZ and 80MHZ

CPMUSYNR_SYNDIV = 0x1;                //FVCO = 2xFREFx(SYNDIV+1)  =  2x16x(1+1) = 64MHZ

CPMUPOSTDIV_POSTDIV = 0x0;            //FPLL = FVCO/(POSTDIV+1) = 64MHZ/(0+1) = 64MHz. FBUS=FPLL/2 = 32MHz

Since CAN bus runs from external oscillator, I am not sure whether this could be a root cause of this issue.

You should configure also acceptance filter, enter into normal mode and potentially also wait for CAN bus synchronization inside your CAN_init() function.

For example:

…

CAN0BTR0 = 0xC3;

CAN0BTR1 = 0x67;

CANIDMR0 = CANIDMR1 = CANIDMR2 = CANIDMR3 = 0xFF;

CANIDMR4 = CANIDMR5 = CANIDMR6 = CANIDMR7 = 0xFF;

CANCTL0  = 0x00;  // restarts MSCAN peripheral

while(CANCTL1 & CANCTL1_INITAK_MASK);  // wait for Initialization Mode exit

while(!(CANCTL0 & CANCTL0_SYNCH_MASK)); // waits for MSCAN synchronization with the CAN bus

}

I hope it helps you.

Have a great day,
RadekS

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Note: If this post answers your question, please click the Correct Answer button. Thank you!
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[thorstenmulun]

Thanks,

i try it now and i get a Massage... more next Week