The mikroC PRO for PIC provides a library (driver) for working with the CAN module.

The CAN is a very robust protocol that has error detection and signalization, self–checking and fault confinement. Faulty CAN data and remote frames are re-transmitted automatically, similar to the Ethernet.

Data transfer rates depends on the distance. For example, 1 Mbit/s can be achieved at network lengths below 40m while 250 Kbit/s can be achieved at network lengths below 250m. The greater distance the lower maximum bitrate that can be achieved. The lowest bitrate defined by the standard is 200Kbit/s. Cables used are shielded twisted pairs.

CAN supports two message formats:

• Standard format, with 11 identifier bits, and
• Extended format, with 29 identifier bits

  Important :

• Consult the CAN standard about CAN bus termination resistance.

Library Routines

• CANSetOperationMode
• CANGetOperationMode
• CANInitialize
• CANSetBaudRate
• CANSetMask
• CANSetFilter
• CANRead
• CANWrite
• CANSetTxIdleLevel

CANSetOperationMode

CANSetOperationMode(_CAN_MODE_CONFIG, 0xFF);

CANGetOperationMode

if (CANGetOperationMode() == _CAN_MODE_NORMAL) { ... };

CANInitialize

if (CAN_CONFIG_FLAGS & _CAN_CONFIG_VALID_XTD_MSG != 0)
  // Set all filters to XTD_MSG
else if (config & _CAN_CONFIG_VALID_STD_MSG != 0)
  // Set all filters to STD_MSG
else
  // Set half of the filters to STD, and the rest to XTD_MSG.

init = _CAN_CONFIG_SAMPLE_THRICE &
       _CAN_CONFIG_PHSEG2_PRG_ON &
       _CAN_CONFIG_STD_MSG       &
       _CAN_CONFIG_DBL_BUFFER_ON &
       _CAN_CONFIG_VALID_XTD_MSG &
       _CAN_CONFIG_LINE_FILTER_OFF;
...
CANInitialize(1, 1, 3, 3, 1, init);   // initialize CAN

CANSetBaudRate

init = _CAN_CONFIG_SAMPLE_THRICE &
       _CAN_CONFIG_PHSEG2_PRG_ON &
       _CAN_CONFIG_STD_MSG       &
       _CAN_CONFIG_DBL_BUFFER_ON &
       _CAN_CONFIG_VALID_XTD_MSG &
       _CAN_CONFIG_LINE_FILTER_OFF;
...
CANSetBaudRate(1, 1, 3, 3, 1, init);

CANSetMask

// Set all mask bits to 1, i.e. all filtered bits are relevant:
CANSetMask(_CAN_MASK_B1, -1, _CAN_CONFIG_XTD_MSG);

// Note that -1 is just a cheaper way to write 0xFFFFFFFF.
   Complement will do the trick and fill it up with ones.

CANSetFilter

// Set id of filter B1_F1 to 3:
CANSetFilter(_CAN_FILTER_B1_F1, 3, _CAN_CONFIG_XTD_MSG);

CANRead

char rcv, rx, len, data[8];
long id;

// ...
rx = 0;
// ...
rcv = CANRead(id, data, len, rx);

CANWrite

char tx, data;
long id;

// ...
tx = _CAN_TX_PRIORITY_0 &
     _CAN_TX_XTD_FRAME;
// ...
CANWrite(id, data, 2, tx);

CANSetTxIdleLevel

CANSetTxIdleLevel(_CAN_DRIVE_HIGH_STATE_ENABLE);

CAN Constants

There is a number of constants predefined in CAN library. To be able to use the library effectively, you need to be familiar with these. You might want to check the example at the end of the chapter.

CAN_OP_MODE

CAN_OP_MODE constants define CAN operation mode. Function CANSetOperationMode expects one of these as its argument:

const char
    _CAN_MODE_BITS   = 0xE0,   // Use this to access opmode  bits
    _CAN_MODE_NORMAL = 0x00,
    _CAN_MODE_SLEEP  = 0x20,
    _CAN_MODE_LOOP   = 0x40,
    _CAN_MODE_LISTEN = 0x60,
    _CAN_MODE_CONFIG = 0x80;

CAN_CONFIG_FLAGS

CAN_CONFIG_FLAGS constants define flags related to CAN module configuration. Functions CANInitialize and CANSetBaudRate expect one of these (or a bitwise combination) as their argument:

const char
    _CAN_CONFIG_DEFAULT         = 0xFF,   // 11111111

    _CAN_CONFIG_PHSEG2_PRG_BIT  = 0x01,
    _CAN_CONFIG_PHSEG2_PRG_ON   = 0xFF,   // XXXXXXX1
    _CAN_CONFIG_PHSEG2_PRG_OFF  = 0xFE,   // XXXXXXX0

    _CAN_CONFIG_LINE_FILTER_BIT = 0x02,
    _CAN_CONFIG_LINE_FILTER_ON  = 0xFF,   // XXXXXX1X
    _CAN_CONFIG_LINE_FILTER_OFF = 0xFD,   // XXXXXX0X

    _CAN_CONFIG_SAMPLE_BIT      = 0x04,
    _CAN_CONFIG_SAMPLE_ONCE     = 0xFF,   // XXXXX1XX
    _CAN_CONFIG_SAMPLE_THRICE   = 0xFB,   // XXXXX0XX

    _CAN_CONFIG_MSG_TYPE_BIT    = 0x08,
    _CAN_CONFIG_STD_MSG         = 0xFF,   // XXXX1XXX
    _CAN_CONFIG_XTD_MSG         = 0xF7,   // XXXX0XXX

    _CAN_CONFIG_DBL_BUFFER_BIT  = 0x10,
    _CAN_CONFIG_DBL_BUFFER_ON   = 0xFF,   // XXX1XXXX
    _CAN_CONFIG_DBL_BUFFER_OFF  = 0xEF,   // XXX0XXXX

    _CAN_CONFIG_MSG_BITS        = 0x60,
    _CAN_CONFIG_ALL_MSG         = 0xFF,   // X11XXXXX
    _CAN_CONFIG_VALID_XTD_MSG   = 0xDF,   // X10XXXXX
    _CAN_CONFIG_VALID_STD_MSG   = 0xBF,   // X01XXXXX
    _CAN_CONFIG_ALL_VALID_MSG   = 0x9F;   // X00XXXXX

You may use bitwise AND (&) to form config byte out of these values. For example:

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init = _CAN_CONFIG_SAMPLE_THRICE &
       _CAN_CONFIG_PHSEG2_PRG_ON &
       _CAN_CONFIG_STD_MSG       &
       _CAN_CONFIG_DBL_BUFFER_ON &
       _CAN_CONFIG_VALID_XTD_MSG &
       _CAN_CONFIG_LINE_FILTER_OFF;
...
CANInitialize(1, 1, 3, 3, 1, init);   // initialize CAN

CAN_TX_MSG_FLAGS

CAN_TX_MSG_FLAGS are flags related to transmission of a CAN message:

const char
    _CAN_TX_PRIORITY_BITS = 0x03,
    _CAN_TX_PRIORITY_0    = 0xFC,   // XXXXXX00
    _CAN_TX_PRIORITY_1    = 0xFD,   // XXXXXX01
    _CAN_TX_PRIORITY_2    = 0xFE,   // XXXXXX10
    _CAN_TX_PRIORITY_3    = 0xFF,   // XXXXXX11

    _CAN_TX_FRAME_BIT    = 0x08,
    _CAN_TX_STD_FRAME    = 0xFF,   // XXXXX1XX
    _CAN_TX_XTD_FRAME    = 0xF7,   // XXXXX0XX

    _CAN_TX_RTR_BIT      = 0x40,
    _CAN_TX_NO_RTR_FRAME = 0xFF,   // X1XXXXXX
    _CAN_TX_RTR_FRAME    = 0xBF;    // X0XXXXXX

You may use bitwise AND (&) to adjust the appropriate flags. For example:

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// form value to be used with CANSendMessage:
send_config = _CAN_TX_PRIORITY_0 &
              _CAN_TX_XTD_FRAME  &
              _CAN_TX_NO_RTR_FRAME;
...
CANSendMessage(id, data, 1, send_config);

CAN_RX_MSG_FLAGS

CAN_RX_MSG_FLAGS are flags related to reception of CAN message. If a particular bit is set; corresponding meaning is TRUE or else it will be FALSE.

const char
    _CAN_RX_FILTER_BITS  = 0x07,  // Use this to access filter bits
    _CAN_RX_FILTER_1     = 0x00,
    _CAN_RX_FILTER_2     = 0x01,
    _CAN_RX_FILTER_3     = 0x02,
    _CAN_RX_FILTER_4     = 0x03,
    _CAN_RX_FILTER_5     = 0x04,
    _CAN_RX_FILTER_6     = 0x05,
    _CAN_RX_OVERFLOW     = 0x08,  // Set if Overflowed else cleared
    _CAN_RX_INVALID_MSG  = 0x10,  // Set if invalid else cleared
    _CAN_RX_XTD_FRAME    = 0x20,  // Set if XTD message else cleared
    _CAN_RX_RTR_FRAME    = 0x40,  // Set if RTR message else cleared
    _CAN_RX_DBL_BUFFERED = 0x80;  // Set if this message was hardware double-buffered

You may use bitwise AND (&) to adjust the appropriate flags. For example:

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if (MsgFlag & _CAN_RX_OVERFLOW != 0) {
  ...
  // Receiver overflow has occurred.
  // We have lost our previous message.
}

CAN_MASK

CAN_MASK constants define mask codes. Function CANSetMask expects one of these as its argument:

#const char
    _CAN_MASK_B1 = 0,
    _CAN_MASK_B2 = 1;

CAN_FILTER

CAN_FILTER constants define filter codes. Function CANSetFilter expects one of these as its argument:

const char
    _CAN_FILTER_B1_F1 = 0,
    _CAN_FILTER_B1_F2 = 1,
    _CAN_FILTER_B2_F1 = 2,
    _CAN_FILTER_B2_F2 = 3,
    _CAN_FILTER_B2_F3 = 4,
    _CAN_FILTER_B2_F4 = 5;

Library Example

This is a simple demonstration of CAN Library routines usage. First node initiates the communication with the second node by sending some data to its address. The second node responds by sending back the data incremented by 1. First node then does the same and sends incremented data back to second node, etc.

Code for the first CAN node:

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unsigned char Can_Init_Flags, Can_Send_Flags, Can_Rcv_Flags; // can flags
unsigned char Rx_Data_Len;                                   // received data length in bytes
char RxTx_Data[8];                                           // can rx/tx data buffer
char Msg_Rcvd;                                               // reception flag
const long ID_1st = 12111, ID_2nd = 3;                       // node IDs
long Rx_ID;

void main() {

  PORTC = 0;                                                // clear PORTC
  TRISC = 0;                                                // set PORTC as output

  Can_Init_Flags = 0;                                       //
  Can_Send_Flags = 0;                                       // clear flags
  Can_Rcv_Flags  = 0;                                       //

  Can_Send_Flags = _CAN_TX_PRIORITY_0 &                     // form value to be used
                   _CAN_TX_XTD_FRAME &                      //     with CANWrite
                   _CAN_TX_NO_RTR_FRAME;

  Can_Init_Flags = _CAN_CONFIG_SAMPLE_THRICE &              // form value to be used
                   _CAN_CONFIG_PHSEG2_PRG_ON &              // with CANInit
                   _CAN_CONFIG_XTD_MSG &
                   _CAN_CONFIG_DBL_BUFFER_ON &
                   _CAN_CONFIG_VALID_XTD_MSG;
  
  CANInitialize(1,3,3,3,1,Can_Init_Flags);                  // Initialize CAN module
  CANSetOperationMode(_CAN_MODE_CONFIG,0xFF);               // set CONFIGURATION mode
  CANSetMask(_CAN_MASK_B1,-1,_CAN_CONFIG_XTD_MSG);          // set all mask1 bits to ones
  CANSetMask(_CAN_MASK_B2,-1,_CAN_CONFIG_XTD_MSG);          // set all mask2 bits to ones
  CANSetFilter(_CAN_FILTER_B2_F4,ID_2nd,_CAN_CONFIG_XTD_MSG);// set id of filter B2_F4 to 2nd node ID

  CANSetOperationMode(_CAN_MODE_NORMAL,0xFF);               // set NORMAL mode

  RxTx_Data[0] = 9;                                         // set initial data to be sent

  CANWrite(ID_1st, RxTx_Data, 1, Can_Send_Flags);           // send initial message

  while(1) {                                                               // endless loop
    Msg_Rcvd = CANRead(&Rx_ID , RxTx_Data , &Rx_Data_Len, &Can_Rcv_Flags); // receive message
    if ((Rx_ID == ID_2nd) && Msg_Rcvd) {                                   // if message received check id
      PORTC = RxTx_Data[0];                                                // id correct, output data at PORTC
      RxTx_Data[0]++ ;                                                     // increment received data
      Delay_ms(10);
      CANWrite(ID_1st, RxTx_Data, 1, Can_Send_Flags);                      // send incremented data back
    }
  }
}

Code for the second CAN node:

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unsigned char Can_Init_Flags, Can_Send_Flags, Can_Rcv_Flags; // can flags
unsigned char Rx_Data_Len;                                   // received data length in bytes
char RxTx_Data[8];                                           // can rx/tx data buffer
char Msg_Rcvd;                                               // reception flag
const long ID_1st = 12111, ID_2nd = 3;                       // node IDs
long Rx_ID;

void main() {

  PORTC = 0;                                                // clear PORTC
  TRISC = 0;                                                // set PORTC as output

  Can_Init_Flags = 0;                                       //
  Can_Send_Flags = 0;                                       // clear flags
  Can_Rcv_Flags  = 0;                                       //

  Can_Send_Flags = _CAN_TX_PRIORITY_0 &                     // form value to be used
                   _CAN_TX_XTD_FRAME &                      //     with CANWrite
                   _CAN_TX_NO_RTR_FRAME;

  Can_Init_Flags = _CAN_CONFIG_SAMPLE_THRICE &              // form value to be used
                   _CAN_CONFIG_PHSEG2_PRG_ON &              // with CANInit
                   _CAN_CONFIG_XTD_MSG &
                   _CAN_CONFIG_DBL_BUFFER_ON &
                   _CAN_CONFIG_VALID_XTD_MSG &
                   _CAN_CONFIG_LINE_FILTER_OFF;

  CANInitialize(1,3,3,3,1,Can_Init_Flags);                  // initialize external CAN module
  CANSetOperationMode(_CAN_MODE_CONFIG,0xFF);               // set CONFIGURATION mode
  CANSetMask(_CAN_MASK_B1,-1,_CAN_CONFIG_XTD_MSG);          // set all mask1 bits to ones
  CANSetMask(_CAN_MASK_B2,-1,_CAN_CONFIG_XTD_MSG);          // set all mask2 bits to ones
  CANSetFilter(_CAN_FILTER_B2_F3,ID_1st,_CAN_CONFIG_XTD_MSG);// set id of filter B2_F3 to 1st node ID

  CANSetOperationMode(_CAN_MODE_NORMAL,0xFF);               // set NORMAL mode

  while (1) {                                                              // endless loop
    Msg_Rcvd = CANRead(&Rx_ID , RxTx_Data , &Rx_Data_Len, &Can_Rcv_Flags); // receive message
    if ((Rx_ID == ID_1st) && Msg_Rcvd) {                                   // if message received check id
      PORTC = RxTx_Data[0];                                                // id correct, output data at PORTC
      RxTx_Data[0]++ ;                                                     // increment received data
      CANWrite(ID_2nd, RxTx_Data, 1, Can_Send_Flags);                      // send incremented data back
    }
  }
}

HW Connection

Example of interfacing CAN transceiver with MCU and bus

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