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Multiple repeat transmissions using Atmel T89C51CC01

Robert McKinley

Hi,

I'm writting code for the above chip. I can receive messages into my application using the CAN simulator no problem.
However, when I launch a message from my application, it is continuously re-transmitted (as seen on the can bus simulator). The TXOK flag is set OK and I get into my interrupt but, the only way I have been able to stop re-transmissions is by setting the CANCONCH register for the page to 0 and disabling the page.
What am I doing wrong, should the simulator mimic a reply ACK to prevent multiple re-transmissions or is it my responsibility to disable further transmissions?

Any clues?

Regards
Rob McKinley

Parents
  • 0 in reply to Oleg Sergeev

    Agree with Oleg,

    also study aplication note 165 from Keil (a little hard to understand, but verry good)

    Example:

    char CanSendIsr (unsigned char ch,  unsigned char *p)  {
  unsigned char i, typ;

// check if CAN message object is defined for transmit
  if (ch >= sizeof (id_typ))      return (-1);
  typ = id_typ[ch];
  if ((typ & CanCONCH) != CanTX)  return (-1);

  i = typ & 0xF;                 // message length

  ECAN = 0;                      // disable CAN interupt

  CANPAGE = CanChannel(ch);      // select CAN message object
  if ((CANCONCH & CanCONCH))  {  // CAN channel busy?
                                 // yes copy to interrupt buffer
    memcpy (outbuf[ostart & (OLEN-1)], p, sizeof(outbuf[0]));
    ostart++;
  }
  else  {                        // not, transfer to message object
    CANCONCH = 0;                // reset previous status
    CANSTCH  = 0;
    while (i)  {                 // copy information to message buffer
      CANMSG = *p++;
      i--;
    }
    CANCONCH = typ;              // send information
  }
  ECAN = 1;                      // enable CAN interupt

  return (0);
}


    Thank you Oleg for your interesting reply.

    Can you detaliate, plz , this phrase:


    Finally, as temporal workaroud: use TTC mode oc CAN macro - it will send a frame only one time even errors occur.


    It sems to be an interesting method, but i dont know nothing about it.

    Thank you again Dear Oleg Sergeev!!

Reply
  • 0 in reply to Oleg Sergeev

    Agree with Oleg,

    also study aplication note 165 from Keil (a little hard to understand, but verry good)

    Example:

    char CanSendIsr (unsigned char ch,  unsigned char *p)  {
  unsigned char i, typ;

// check if CAN message object is defined for transmit
  if (ch >= sizeof (id_typ))      return (-1);
  typ = id_typ[ch];
  if ((typ & CanCONCH) != CanTX)  return (-1);

  i = typ & 0xF;                 // message length

  ECAN = 0;                      // disable CAN interupt

  CANPAGE = CanChannel(ch);      // select CAN message object
  if ((CANCONCH & CanCONCH))  {  // CAN channel busy?
                                 // yes copy to interrupt buffer
    memcpy (outbuf[ostart & (OLEN-1)], p, sizeof(outbuf[0]));
    ostart++;
  }
  else  {                        // not, transfer to message object
    CANCONCH = 0;                // reset previous status
    CANSTCH  = 0;
    while (i)  {                 // copy information to message buffer
      CANMSG = *p++;
      i--;
    }
    CANCONCH = typ;              // send information
  }
  ECAN = 1;                      // enable CAN interupt

  return (0);
}


    Thank you Oleg for your interesting reply.

    Can you detaliate, plz , this phrase:


    Finally, as temporal workaroud: use TTC mode oc CAN macro - it will send a frame only one time even errors occur.


    It sems to be an interesting method, but i dont know nothing about it.

    Thank you again Dear Oleg Sergeev!!

Children
  • 0 in reply to marcu andy

    Hi,

    TTC (time-triggered communication) mode has been announced via ISO11898 standard.
    In this mode any node sends message(s) inside own time slot.
    In short, nodes listen for a sync message. When it has been detected, each node sets own delay (by your program - timer, cycle, etc) and after this pause sends a frame to the net. So by this method you may create a very stable net which will work even if alot of messages are transmitted there because the bus arbitration method will not block nodes with low priority identifiers (see: each node has own time slot). As side effect, if any error occurs then node cannot resend message itself because its time-slot has been gone. Instead it, software should wait till next sync message and resend a frame again inside own time-slot.

    Thanks for Temic/Atmel, the T89C51CC01 does support this method (TTC bit in CANGCON register). Manual says that CAN macro in TTC mode will send a frame only one time even errors occur.
    Hmm, my tests show that if no ACK bit detected then CAN macro try to send a frame again till TEC<127 even in TTC mode. Now I am clearing up this question with Atmel.

    Good days!