CANPAGE = CanChannel(ch);      // select CAN message object

  if (!(CANSTCH & CanRXOK)) {
    return (-2);                 // no message available
  }

  if (CANSTCH & CanDLCW)  {
    return (-2);                 // incoming message does not have expected length
  }

  CANCONCH = 0;                  // reset previous status
  CANSTCH  = 0;
  while (i)  {                   // copy information to message buffer
    *p++ = CANMSG;
    i--;
  }
  CANCONCH = typ;                // set channel for new receiving
  return (0);                    // message object copied to buffer
}

/***** CAN I/O Routines for Remote Frame Handling **********************************/

/*
 * CanReqRemote:   Request Remote Frame
 *   Input Parameter:  ch :=  message object channel (0 .. 14)
 *
 *   Return Value:      0     n bytes of message transferred to data buffer
 *                     -1     message object not defined for transmission
 *               
 *    - check if CAN message object is defined for transmission
 *    - set message object for remote frame request
 */
char CanReqRemote (unsigned char ch)  {
  unsigned char typ;

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

  CANPAGE = CanChannel(ch);      // select CAN message object
  CANCONCH = 0;                  // reset previous status
  CANSTCH  = 0;
  CANIDT4 |= CanRTRMSK;          // Set Remote transmission request value
  CANCONCH = typ;                // set channel for transmission
  return (0);
}


/*
 * CanGetRemote:   Get Data from Remote Frame Request
 *   Input Parameter:  ch :=  message object channel (0 .. 14)
 *                      p :=  pointer to data buffer
 *
 *   Return Value:      0     n bytes of message transferred to data buffer
 *                     -1     message object not defined for transmission
 *                     -2     incoming message does not have expected length
 *                     -3     no remote message received
 *               
 *    - check if CAN message object is defined for transmission
 *    - check if a message is received
 *    - copy received message to data buffer
 */
char CanGetRemote (unsigned char ch,  unsigned char *p)  {
  unsigned char i, typ;

// check if CAN message object is defined for transmission
  if (ch >= sizeof (id_typ))      return (-1);
  typ = id_typ[ch];
  if ((typ & CanCONCH) != CanTX)  return (-1);
  i = typ & 0xF;                 // message length

  CANPAGE = CanChannel(ch);      // select CAN message object
  if (!(CANSTCH & CanRXOK)) {
    return (-3);                 // no CAN message received
  }

  if (CANSTCH & CanDLCW)  {
    return (-2);                 // incoming message does not have expected length
  }

  CANCONCH = 0;                  // reset previous status
  CANSTCH  = 0;
  while (i)  {                   // copy information to message buffer
    *p++ = CANMSG;
    i--;
  }
  return (0);                    // message object copied to buffer
}


#pragma NOAREGS                  // function called from interrupt, no ARx symbols!
/*
 * CanSetRemote:
 *   Input Parameter:  ch :=  message object channel (0 .. 14)
 *                      p :=  pointer to data buffer
 *
 *    - check if CAN message object is defined for remote reply
 *    - Fil data buffer with data
 */
char CanSetRemote (unsigned char ch,  unsigned char *p)  {
  unsigned char i, typ;
  unsigned char save_canpage;

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

  i = typ & 0xF;                 // message length
  
  save_canpage = CANPAGE;        // Save the current CANPAGE (to work in parallel with polling mode)
  CANPAGE = CanChannel(ch);      // select CAN message object

  CANCONCH &= ~CanRPLV;          // reset information valid

  while (i)  {                   // copy information to message buffer
    CANMSG = *p++;
    i--;
  }
  CANCONCH |= CanRPLV;           // set information valid
  CANPAGE = save_canpage;        // restore the old CAN page (required for polling mode)

  return (0);                    // message object copied to buffer
}
  
#pragma AREGS

/***** Interrupt Driven CAN I/O Routines *************************************/

// definitions for transmit (output) buffer (CAN Message Object 2)
#define  OLEN  16                     // number of buffers in outbuf
unsigned char  ostart = 0;            // transmission buffer start index
unsigned char  oend = 0;              // transmission buffer end index
unsigned char  xdata outbuf[OLEN][8]; // transmission buffer
bit            tx_error;              // set when transmit error occur

// definitions for receive (input) buffer (CAN Message Object 3)
#define  ILEN  16                     // number of buffers in inbuf
unsigned char  istart = 0;            // receive buffer start index
unsigned char  iend = 0;              // receive buffer end index
unsigned char xdata inbuf[ILEN][8];   // receive buffer
bit            rx_error;              // set when receive error occur


#pragma REGISTERBANK (1)              // function called from Register Bank 1
/*
 * Read Data into inbuf (for CAN channels handled by Interrupt
 */
static void ReadToInBuf (void)  {
  unsigned char i;
  unsigned char xdata *p;

  if (!(CANSTCH & CanRXOK))  {
    rx_error = 1;                   // not a receive OK interrupt
  }

  CANCONCH = 0;                     // reset previous status
  CANSTCH  = 0;

  p = inbuf[istart & (ILEN-1)];
  istart++;
  for (i = sizeof (inbuf[0]); i != 0; i--)  {  // copy information to message buffer
    *p = CANMSG;
    p++;
  }

  CANCONCH = ID3TYP;                // set channel for new receiving
}


/*
 * CanInterrupt: 
 *   - called by hardware when a CAN message is send or received
 *   - checks if Channel 2 interrupt (transmission) occured
 *      - if new transmit data, copy new data to Channel 2 object buffers
 *   - checks if Channel 3 interrupt (receiving) occured
 *      - copy received data, copy data from Channel 3 object buffers
 */

void CanInterrupt (void) interrupt 7 using 1  {
  unsigned char i;
  unsigned char typ;
  unsigned char save_canpage;
  unsigned char xdata *p;
  
  save_canpage = CANPAGE;           // Save the current CANPAGE (to work in parallel with polling mode)

// Handle Interrupt for Transmit Channel 2
  if (ID2IntChk)   {                // Check Channel 2 Interrupt (transmit buffer)
    CANPAGE = CanChannel(2);
    if (!(CANSTCH & CanTXOK)) {
      tx_error = 1;                 // not a transmit OK interrupt
    }

    CANCONCH = 0;                   // reset previous status
    CANSTCH  = 0;
    if (ostart != oend)  {
      p = outbuf[oend & (OLEN-1)];
      oend++;
      typ = id_typ[2];
      i = typ & 0xF;                 // message length

      while (i)  {                   // copy information to message buffer
        CANMSG = *p;
        p++;
        i--;
      }
      CANCONCH = typ;                // send information
    }
  }


// Handle Interrupt for Receive Channel 3/4
  if (ID4IntChk)   {                // Check if data are available in Channel 4
    CANPAGE = CanChannel (4);
    ReadToInBuf ();                 // Read Data into inbuf
  }

  if (ID3IntChk)   {                // Check if data are available in Channel 4
    CANPAGE = CanChannel (3);
    ReadToInBuf ();                 // Read Data into inbuf
  }

  CANPAGE = save_canpage;          // restore the old CAN page (required for polling mode)
}

#pragma REGISTERBANK (0)           // use Register Bank 0 for following code



/*
 * CanSendIsr:
 *   Input Parameter:  ch :=  message object channel (0 .. 14)
 *                      p :=  pointer to data buffer
 *
 *   Return Value:      0     n bytes of message transferred to data buffer
 *                     -1     message object not defined for transmission
 *                     -2     no message available
 *                     -3     messsage data length differs from definition
 *               
 *    - check if CAN message object is defined for receiving
 *    - check if a message is received
 *    - copy received message to data buffer
 *    - set message object for receiving
 */
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);
}



/*
 * CanReadIsr:
 *   Input Parameter:  ch :=  message object channel (0 .. 14)
 *                      p :=  pointer to data buffer
 *
 *   Return Value:      0     n bytes of message transferred to data buffer
 *                     -1     message object not defined for receiving
 *                     -2     no data available
 *               
 *    - check if CAN message object is defined for receiving
 *    - check if a message is received
 *    - copy received message to data buffer
 *    - set message object for receiving
 */
char CanReadIsr (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

  if (istart == iend)             return (-2);
  memcpy (p, inbuf[iend & (ILEN-1)], i);
  iend++;
  return (0);
}