Freescale MC9S12X: CAN Receive Configuration

1. MSCAN receiving process

Detect receive flag: The CANRFLG register is used here.

Detect frame mode (standard frame/extended frame): The CANIDR register is used here.

Read identifier: The CANIDR register is used here.

Determine the frame format (remote frame/data frame): The CANIDR register is used here.

Read data length: The CANDLR register is used here.

Read data: The CANDSR register is used here.

Clear the receive flag: The CANTFLG register is used here.

2. Introduction to MSCAN Receive Register

There are two types of CANIDR registers: standard frame type and extended frame type.

Standard frame type:

Extended frame type:

3. CAN receiving configuration specific program implementation

1. Standard frame program

The specific code is as follows:

struct can_msg //Message structure

{

    unsigned int id; //帧ID

    unsigned char RTR; // RTR: 1 for remote frame, 0 for data frame

    unsigned char data[8]; //frame data

    unsigned char len; //data length

    unsigned char prty; //priority

};

/*************************************************************/

/* CAN0 receiving */

/*************************************************************/

int MSCAN0_Receive(struct can_msg *msg)

{

  unsigned char sp2;

  // Check the reception flag

  if(!(CAN0RFLG_RXF))

    return(FALSE);

  // Detect CAN protocol message mode (general/extended) identifier

  if(CAN0RXIDR1_IDE) //0 is standard format, 1 is extended format

    // IDE = Recessive (Extended Mode)

    return(FALSE);

  // Read the identifier

  msg.id = (unsigned int)(CAN0RXIDR0<<3) | 

            (unsigned char)(CAN0RXIDR1>>5);

  if(CAN0RXIDR1&0x10)

    msg.RTR = TRUE;

  else

    msg.RTR = FALSE;

  // Read data length 

  msg.len = CAN0RXDLR;

  // Read data

  for(sp2 = 0; sp2 < msg.len; sp2++)

    msg.data[sp2] = *((&CAN0RXDSR0)+sp2);

  // Clear RXF flag (buffer is ready to receive)

  CAN0RFLG = 0x01;

  return(TRUE);

}

2. Extended frame program

The specific code is as follows:

struct can_msg //Message structure

{

    unsigned long ID; //帧ID

    unsigned char RTR; // RTR: 1 for remote frame, 0 for data frame

    unsigned char data[8]; //frame data

    unsigned char len; //data length

    unsigned char prty; //priority

};

/*************************************************************/

/* CAN0 receiving */

/*************************************************************/

int MSCAN0_Receive(struct can_msg *msg)

{

  unsigned char sp2;

  // Check the reception flag

  if(!(CAN0RFLG_RXF))

    return(FALSE);

  // Detect CAN protocol message mode (general/extended) identifier

  if(!CAN0RXIDR1_IDE) //0 is standard format, 1 is extended format

    // IDE = Recessive (Extended Mode)

    return(FALSE);

  // Read the identifier

  msg.ID = ((unsigned long)(CAN1RXIDR0&0xff))<<21;

  msg.ID = can1_msg_get.ID & ((unsigned long)0xff<<21);

  msg.ID = can1_msg_get.ID | (((unsigned long)(CAN1RXIDR1&0xe0))<<13);

  msg.ID = can1_msg_get.ID | (((unsigned long)(CAN1RXIDR1&0x07))<<15);

  msg.ID = can1_msg_get.ID | (((unsigned long)(CAN1RXIDR2&0xff))<<7);  

  msg.ID = can1_msg_get.ID | (((unsigned long)(CAN1RXIDR3&0xfe))>>1); 

  if(CAN0RXIDR3&0x01)

    msg.RTR = TRUE;

  else

    msg.RTR = FALSE;

  // Read data length 

  msg.len = CAN0RXDLR;

  // Read data

  for(sp2 = 0; sp2 < msg.len; sp2++)

    msg.data[sp2] = *((&CAN0RXDSR0)+sp2);

  // Clear RXF flag (buffer is ready to receive)

  CAN0RFLG = 0x01;

  return(TRUE);

}