The SPI module is available with a number of the AVR compliant MCUs. The mikroC PRO for AVR provides a library (driver) for working with mikroElektronika's CANSPI Add-on boards (with MCP2515 or MCP2510) via SPI interface.

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 depend on 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.
• An effective CANSPI communication speed depends on SPI and certainly is slower than “real” CAN.
• The library uses the SPI module for communication. User must initialize appropriate SPI module before using the CANSPI Library.
• For MCUs with two SPI modules it is possible to initialize both of them and then switch by using the SPI_Set_Active routine.
• CANSPI module refers to mikroElektronika's CANSPI Add-on board connected to SPI module of MCU.

Library Dependency Tree

External dependencies of CANSPI Library

Library Routines

• CANSPISetOperationMode
• CANSPIGetOperationMode
• CANSPIInitialize
• CANSPISetBaudRate
• CANSPISetMask
• CANSPISetFilter
• CANSPIRead
• CANSPIWrite

CANSPISetOperationMode

// set the CANSPI module into configuration mode (wait inside CANSPISetOperationMode until this mode is set)
CANSPISetOperationMode(_CANSPI_MODE_CONFIG, 0xFF);

CANSPIGetOperationMode

// check whether the CANSPI module is in Normal mode and if it is do something.
if (CANSPIGetOperationMode() == _CANSPI_MODE_NORMAL) {
  ...
}

CANSPIInitialize

// CANSPI module connections
sbit CanSpi_CS  at  PORTB0_bit;
sbit CanSpi_CS_Direction  at  DDB0_bit;
sbit CanSpi_Rst at  PORTB2_bit;
sbit CanSpi_Rst_Direction at  DDB0_bit;
// End CANSPI module connections

// initialize the CANSPI module with the appropriate baud rate and message acceptance flags along with the sampling rules
char CanSPi_Init_Flags;
  ...  
  CanSPi_Init_Flags = _CANSPI_CONFIG_SAMPLE_THRICE &  // form value to be used
                   _CANSPI_CONFIG_PHSEG2_PRG_ON &  // with CANSPIInitialize
                   _CANSPI_CONFIG_XTD_MSG &
                   _CANSPI_CONFIG_DBL_BUFFER_ON &
                   _CANSPI_CONFIG_VALID_XTD_MSG;
  ...
  SPI1_Init();                                // initialize SPI module
  CANSPIInitialize(1,3,3,3,1,CanSpi_Init_Flags);  // initialize external CANSPI module

CANSPISetBaudRate

// set required baud rate and sampling rules
char canspi_config_flags;
...  
CANSPISetOperationMode(CANSPI_MODE_CONFIG,0xFF);              // set CONFIGURATION mode (CANSPI module mast be in config mode for baud rate settings)
canspi_config_flags = _CANSPI_CONFIG_SAMPLE_THRICE &
                   _CANSPI_CONFIG_PHSEG2_PRG_ON &
                   _CANSPI_CONFIG_STD_MSG       &
                   _CANSPI_CONFIG_DBL_BUFFER_ON &
                   _CANSPI_CONFIG_VALID_XTD_MSG &
                   _CANSPI_CONFIG_LINE_FILTER_OFF;
CANSPISetBaudRate(1, 1, 3, 3, 1, canspi_config_flags);

CANSPISetMask

// set the appropriate filter mask and message type value
CANSPISetOperationMode(_CANSPI_MODE_CONFIG,0xFF);              // set CONFIGURATION mode (CANSPI module must be in config mode for mask settings)

// Set all B1 mask bits to 1 (all filtered bits are relevant):
// Note that -1 is just a cheaper way to write 0xFFFFFFFF.
// Complement will do the trick and fill it up with ones.
CANSPISetMask(_CANSPI_MASK_B1, -1, _CANSPI_CONFIG_MATCH_MSG_TYPE & _CANSPI_CONFIG_XTD_MSG);

CANSPISetFilter

// set the appropriate filter value and message type
CANSPISetOperationMode(_CANSPI_MODE_CONFIG,0xFF);                  // set CONFIGURATION mode (CANSPI module must be in config mode for filter settings)

// Set id of filter B1_F1 to 3: 
CANSPISetFilter(_CANSPI_FILTER_B1_F1, 3, _CANSPI_CONFIG_XTD_MSG);

CANSPIRead

// check the CANSPI module for received messages. If any was received do something. 
char msg_rcvd, rx_flags, data_len;
char data[8];
long msg_id;
...
CANSPISetOperationMode(_CANSPI_MODE_NORMAL,0xFF);                  // set NORMAL mode (CANSPI module must be in mode in which receive is possible)
...
rx_flags = 0;                                                // clear message flags
if (msg_rcvd = CANSPIRead(msg_id, data, data_len, rx_flags)) {
  ...
}

CANSPIWrite

// send message extended CAN message with the appropriate ID and data
char tx_flags;
char data[8];
long msg_id;
...
CANSPISetOperationMode(_CANSPI_MODE_NORMAL,0xFF);                  // set NORMAL mode (CANSPI must be in mode in which transmission is possible)

tx_flags = _CANSPI_TX_PRIORITY_0 & _CANSPI_TX_XTD_FRAME;             // set message flags
CANSPIWrite(msg_id, data, 2, tx_flags);

CANSPI Constants

There is a number of constants predefined in the CANSPI library. You need to be familiar with them in order to be able to use the library effectively. Check the example at the end of the chapter.

CANSPI_OP_MODE

The CANSPI_OP_MODE constants define CANSPI operation mode. Function CANSPISetOperationMode expects one of these as it's argument:

const char
    _CANSPI_MODE_BITS   = 0xE0,   // Use this to access opmode  bits
    _CANSPI_MODE_NORMAL = 0x00,
    _CANSPI_MODE_SLEEP  = 0x20,
    _CANSPI_MODE_LOOP   = 0x40,
    _CANSPI_MODE_LISTEN = 0x60,
    _CANSPI_MODE_CONFIG = 0x80;

CANSPI_CONFIG_FLAGS

The CANSPI_CONFIG_FLAGS constants define flags related to the CANSPI module configuration. The functions CANSPIInitialize, CANSPISetBaudRate, CANSPISetMask and CANSPISetFilter expect one of these (or a bitwise combination) as their argument:

const char
    _CANSPI_CONFIG_DEFAULT         = 0xFF,   // 11111111

    _CANSPI_CONFIG_PHSEG2_PRG_BIT  = 0x01,
    _CANSPI_CONFIG_PHSEG2_PRG_ON   = 0xFF,   // XXXXXXX1
    _CANSPI_CONFIG_PHSEG2_PRG_OFF  = 0xFE,   // XXXXXXX0

    _CANSPI_CONFIG_LINE_FILTER_BIT = 0x02,
    _CANSPI_CONFIG_LINE_FILTER_ON  = 0xFF,   // XXXXXX1X
    _CANSPI_CONFIG_LINE_FILTER_OFF = 0xFD,   // XXXXXX0X

    _CANSPI_CONFIG_SAMPLE_BIT      = 0x04,
    _CANSPI_CONFIG_SAMPLE_ONCE     = 0xFF,   // XXXXX1XX
    _CANSPI_CONFIG_SAMPLE_THRICE   = 0xFB,   // XXXXX0XX

    _CANSPI_CONFIG_MSG_TYPE_BIT    = 0x08,
    _CANSPI_CONFIG_STD_MSG         = 0xFF,   // XXXX1XXX
    _CANSPI_CONFIG_XTD_MSG         = 0xF7,   // XXXX0XXX

    _CANSPI_CONFIG_DBL_BUFFER_BIT  = 0x10,
    _CANSPI_CONFIG_DBL_BUFFER_ON   = 0xFF,   // XXX1XXXX
    _CANSPI_CONFIG_DBL_BUFFER_OFF  = 0xEF,   // XXX0XXXX

    _CANSPI_CONFIG_MSG_BITS        = 0x60,
    _CANSPI_CONFIG_ALL_MSG         = 0xFF,   // X11XXXXX
    _CANSPI_CONFIG_VALID_XTD_MSG   = 0xDF,   // X10XXXXX
    _CANSPI_CONFIG_VALID_STD_MSG   = 0xBF,   // X01XXXXX
    _CANSPI_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 = _CANSPI_CONFIG_SAMPLE_THRICE &
       _CANSPI_CONFIG_PHSEG2_PRG_ON &
       _CANSPI_CONFIG_STD_MSG       &
       _CANSPI_CONFIG_DBL_BUFFER_ON &
       _CANSPI_CONFIG_VALID_XTD_MSG &
       _CANSPI_CONFIG_LINE_FILTER_OFF;
...
CANSPIInitialize(1, 1, 3, 3, 1, init);   // initialize CANSPI

CANSPI_TX_MSG_FLAGS

CANSPI_TX_MSG_FLAGS are flags related to transmission of a CAN message:

const char
    _CANSPI_TX_PRIORITY_BITS = 0x03,
    _CANSPI_TX_PRIORITY_0    = 0xFC,   // XXXXXX00
    _CANSPI_TX_PRIORITY_1    = 0xFD,   // XXXXXX01
    _CANSPI_TX_PRIORITY_2    = 0xFE,   // XXXXXX10
    _CANSPI_TX_PRIORITY_3    = 0xFF,   // XXXXXX11

    _CANSPI_TX_FRAME_BIT    = 0x08,
    _CANSPI_TX_STD_FRAME    = 0xFF,    // XXXXX1XX
    _CANSPI_TX_XTD_FRAME    = 0xF7,    // XXXXX0XX

    _CANSPI_TX_RTR_BIT      = 0x40,
    _CANSPI_TX_NO_RTR_FRAME = 0xFF,    // X1XXXXXX
    _CANSPI_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 as sending message flag : */
send_config = _CANSPI_TX_PRIORITY_0 &
              _CANSPI_TX_XTD_FRAME  &
              _CANSPI_TX_NO_RTR_FRAME;
...
CANSPIWrite(id, data, 1, send_config);

CANSPI_RX_MSG_FLAGS

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

const char
    _CANSPI_RX_FILTER_BITS = 0x07,   // Use this to access filter bits
    _CANSPI_RX_FILTER_1    = 0x00,
    _CANSPI_RX_FILTER_2    = 0x01,
    _CANSPI_RX_FILTER_3    = 0x02,
    _CANSPI_RX_FILTER_4    = 0x03,
    _CANSPI_RX_FILTER_5    = 0x04,
    _CANSPI_RX_FILTER_6    = 0x05,

    _CANSPI_RX_OVERFLOW    = 0x08,   // Set if Overflowed else cleared
    _CANSPI_RX_INVALID_MSG = 0x10,   // Set if invalid else cleared
    _CANSPI_RX_XTD_FRAME   = 0x20,   // Set if XTD message else cleared
    _CANSPI_RX_RTR_FRAME    = 0x40,  // Set if RTR message else cleared
    _CANSPI_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 & _CANSPI_RX_OVERFLOW != 0) {
  ...
  // Receiver overflow has occurred.
  // We have lost our previous message.
}

CANSPI_MASK

The CANSPI_MASK constants define mask codes. Function CANSPISetMask expects one of these as it's argument:

const char
    _CANSPI_MASK_B1 = 0,
    _CANSPI_MASK_B2 = 1;

CANSPI_FILTER

The CANSPI_FILTER constants define filter codes. Functions CANSPISetFilter expects one of these as it's argument:

const char
    _CANSPI_FILTER_B1_F1 = 0,
    _CANSPI_FILTER_B1_F2 = 1,
    _CANSPI_FILTER_B2_F1 = 2,
    _CANSPI_FILTER_B2_F2 = 3,
    _CANSPI_FILTER_B2_F3 = 4,
    _CANSPI_FILTER_B2_F4 = 5;

Library Example

This is a simple demonstration of CANSPI 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 CANSPI 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;

// CANSPI module connections
sbit CanSpi_CS  at  PORTB0_bit;
sbit CanSpi_CS_Direction  at  DDB0_bit;
sbit CanSpi_Rst at  PORTB2_bit;
sbit CanSpi_Rst_Direction at  DDB2_bit;
// End CANSPI module connections

void main() {

  PORTC = 0;                                                 // clear PORTC
  DDRC = 255;                                                // set PORTC as output

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

  Can_Send_Flags = _CANSPI_TX_PRIORITY_0 &                   // form value to be used
                   _CANSPI_TX_XTD_FRAME &                    //     with CANSPIWrite
                   _CANSPI_TX_NO_RTR_FRAME;

  Can_Init_Flags = _CANSPI_CONFIG_SAMPLE_THRICE &            // form value to be used
                   _CANSPI_CONFIG_PHSEG2_PRG_ON &            // with CANSPIInit
                   _CANSPI_CONFIG_XTD_MSG &
                   _CANSPI_CONFIG_DBL_BUFFER_ON &
                   _CANSPI_CONFIG_VALID_XTD_MSG;
  

  SPI1_Init();                                                     // initialize SPI1 module

  CANSPIInitialize(1,3,3,3,1,Can_Init_Flags);                      // Initialize external CANSPI module
  CANSPISetOperationMode(_CANSPI_MODE_CONFIG,0xFF);                // set CONFIGURATION mode
  CANSPISetMask(_CANSPI_MASK_B1,-1,_CANSPI_CONFIG_XTD_MSG);        // set all mask1 bits to ones
  CANSPISetMask(_CANSPI_MASK_B2,-1,_CANSPI_CONFIG_XTD_MSG);        // set all mask2 bits to ones
  CANSPISetFilter(_CANSPI_FILTER_B2_F4,ID_2nd,_CANSPI_CONFIG_XTD_MSG);// set id of filter B2_F4 to 2nd node ID

  CANSPISetOperationMode(_CANSPI_MODE_NORMAL,0xFF);                // set NORMAL mode

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

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

  while(1) {                                                                 // endless loop
    Msg_Rcvd = CANSPIRead(&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);
      CANSPIWrite(ID_1st, RxTx_Data, 1, Can_Send_Flags);                     // send incremented data back
    }
  }
}

Code for the second CANSPI 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;

// CANSPI module connections
sbit CanSpi_CS  at  PORTB0_bit;
sbit CanSpi_CS_Direction  at  DDB0_bit;
sbit CanSpi_Rst at  PORTB2_bit;
sbit CanSpi_Rst_Direction at  DDB2_bit;
// End CANSPI module connections

void main() {

  PORTC = 0;                                                  // clear PORTC
  DDRC  = 0xFF;                                               // set PORTC as output

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

  Can_Send_Flags = _CANSPI_TX_PRIORITY_0 &                    // form value to be used
                   _CANSPI_TX_XTD_FRAME &                     //   with CANSPIWrite
                   _CANSPI_TX_NO_RTR_FRAME;

  Can_Init_Flags = _CANSPI_CONFIG_SAMPLE_THRICE &             // Form value to be used
                   _CANSPI_CONFIG_PHSEG2_PRG_ON &             //  with CANSPIInit
                   _CANSPI_CONFIG_XTD_MSG &
                   _CANSPI_CONFIG_DBL_BUFFER_ON &
                   _CANSPI_CONFIG_VALID_XTD_MSG &
                   _CANSPI_CONFIG_LINE_FILTER_OFF;

  SPI1_Init();                                                                // initialize SPI1 module
  
  CANSPIInitialize(1,3,3,3,1,Can_Init_Flags);                                 // initialize external CANSPI module
  CANSPISetOperationMode(_CANSPI_MODE_CONFIG,0xFF);                           // set CONFIGURATION mode
  CANSPISetMask(_CANSPI_MASK_B1,-1,_CANSPI_CONFIG_XTD_MSG);                   // set all mask1 bits to ones
  CANSPISetMask(_CANSPI_MASK_B2,-1,_CANSPI_CONFIG_XTD_MSG);                   // set all mask2 bits to ones
  CANSPISetFilter(_CANSPI_FILTER_B2_F3,ID_1st,_CANSPI_CONFIG_XTD_MSG);        // set id of filter B2_F3 to 1st node ID

  CANSPISetOperationMode(_CANSPI_MODE_NORMAL,0xFF);                           // set NORMAL mode

  while (1) {                                                                 // endless loop
    Msg_Rcvd = CANSPIRead(&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
      CANSPIWrite(ID_2nd, RxTx_Data, 1, Can_Send_Flags);                      // send incremented data back
    }
  }
}

HW Connection

Example of interfacing CAN transceiver MCP2510 with MCU via SPI interface

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