Using CAN bus with (not just NUCLEO) mbed boards

Dependencies:   mbed CANMsg

Using CAN bus with mbed boards

Two low cost STM32F103C8T6 boards are connected to the same CAN bus via transceivers (MCP2551 or TJA1040, or etc.). CAN transceivers are not part of NUCLEO boards, therefore must be added by us. Remember also that CAN bus (even a short one) must be terminated with 120 Ohm resitors at both ends. Although there seems to be an alternative solution.

Schematic

Zoom in

/media/uploads/hudakz/stm32f103c8t6_can_hello.png

Hookup

/media/uploads/hudakz/20150724_080148.jpg

The mbed boards in this example are transmitting CAN messages carrying two data items:

uint8_t   counter;  // one byte
float     voltage;  // four bytes

So in this case the total length of payload data is five bytes (must not exceed eight bytes).
For our convenience, the "<<" (append) operator (defined in CANMsg library) is used to add data to the CAN message.
The usage of "<<" and ">>" operators is similar to the C++ io-streams operators. We can append data one at a time

txMsg << counter;
txMsg << voltage;

or combine all into one expression.

txMsg << counter << voltage;

The actual data length of a CAN message is automatically updated when using "<<" or ">>" operators.
After successful transmission the CAN message is printed to the serial terminal of the connected PC. So we can check the details (ID, type, format, length and raw data). If something goes wrong during transmission a "Transmission error" message is printed to the serial terminal.

On arrival of a CAN message it's also printed to the serial terminal of the connected PC. So we can see the details (ID, type, format, length and raw data). Then its ID is checked. If there is a match with the ID of awaited message then data is extracted from the CAN message (in the same sequence as it was appended before transmitting) using the ">>" (extract) operator one at a time

rxMsg >> counter;
rxMsg >> voltage;

or all in one shot

rxMsg >> counter >> voltage;


The same source code is used for both boards, but:

  • For board #1 compile the example without any change to main.cpp
  • For board #2 comment out the line #define BOARD1 1 before compiling

Once binaries have been downloaded to the boards reset both board at the same time.

NOTE:

The code published here was written for the official NUCLEO boards. When using STM32F103C8T6 boards, shown in the picture above (on-board LED is active on 0),

  • Include (uncomment) the line #define TARGET_STM32F103C8T6 1
  • Select NUCLEO-F103RB as target platform for the online compiler.

CAN bus related information

main.cpp

Committer:
hudakz
Date:
7 months ago
Revision:
9:3211e88e30a5
Parent:
8:c65afde7f7f5

File content as of revision 9:3211e88e30a5:

/*
 * An example showing how to use the mbed CAN API:
 *
 * Two affordable (about $2 on ebay) STM32F103C8T6 boards (20kB SRAM, 64kB Flash),
 * (see [https://developer.mbed.org/users/hudakz/code/STM32F103C8T6_Hello/] for more details)
 * are connected to the same CAN bus via transceivers (MCP2551 or TJA1040, or etc.).
 * CAN transceivers are not part of NUCLEO boards, therefore must be added by you.
 * Remember also that CAN bus (even a short one) must be terminated with 120 Ohm resitors at both ends.
 *
 *
 * The same code is used for both mbed boards, but:
 *      For board #1 compile the example without any change.
 *      For board #2 comment out line 21 before compiling
 *
 * Once the binaries have been downloaded to the boards reset both boards at the same time.
 *
 */

//#define TARGET_STM32F103C8T6    1       // uncomment this line to use STM32F103C8T6 boards

#define BOARD1                  1       // comment out this line when compiling for board #2

#if defined(TARGET_STM32F103C8T6)
    #define LED_PIN     PC_13
    const int           OFF = 1;
    const int           ON = 0;
#else
    #define LED_PIN     LED1
    const int           OFF = 0;
    const int           ON = 1;
#endif

#if defined(BOARD1)
    const unsigned int  RX_ID = 0x100;
    const unsigned int  TX_ID = 0x101;
#else
    const unsigned int  RX_ID = 0x101;
    const unsigned int  TX_ID = 0x100;
#endif

#include "mbed.h"
#include "CANMsg.h"

Serial              pc(USBTX, USBRX);
CAN                 can(PB_8, PB_9);  // CAN Rx pin name, CAN Tx pin name
//CAN                 can(p30, p29);  // CAN Rx pin name, CAN Tx pin name
CANMsg              rxMsg;
CANMsg              txMsg;
DigitalOut          led(LED_PIN);
Timer               timer;
uint8_t             counter = 0;
AnalogIn            analogIn(A0);
float               voltage;

/**
 * @brief   Prints CAN message to PC's serial terminal
 * @note
 * @param   CANMessage to print
 * @retval
 */
void printMsg(CANMessage& msg)
{
    pc.printf("  ID      = 0x%.3x\r\n", msg.id);
    pc.printf("  Type    = %d\r\n", msg.type);
    pc.printf("  Format  = %d\r\n", msg.format);
    pc.printf("  Length  = %d\r\n", msg.len);
    pc.printf("  Data    =");
    for(int i = 0; i < msg.len; i++)
        pc.printf(" 0x%.2X", msg.data[i]);
    pc.printf("\r\n");
}

/**
 * @brief   Handles received CAN messages
 * @note    Called on 'CAN message received' interrupt.
 * @param
 * @retval
 */
void onCanReceived(void)
{
    can.read(rxMsg);
    pc.printf("-------------------------------------\r\n");
    pc.printf("CAN message received\r\n");
    printMsg(rxMsg);

    if (rxMsg.id == RX_ID) {
        // extract data from the received CAN message 
        // in the same order as it was added on the transmitter side
        rxMsg >> counter;
        rxMsg >> voltage;    
        pc.printf("  counter = %d\r\n", counter);
        pc.printf("  voltage = %e V\r\n", voltage);
    }
    timer.start(); // to transmit next message in main
}


/**
 * @brief   Main
 * @note
 * @param
 * @retval
 */
int main(void)
{
    pc.baud(9600);          // set serial speed
    can.frequency(1000000); // set CAN bit rate to 1Mbps
    can.filter(RX_ID, 0xFFF, CANStandard, 0); // set filter #0 to accept only standard messages with ID == RX_ID
    can.attach(onCanReceived);                // attach ISR to handle received messages

#if defined(BOARD1)
    led = ON;               // turn the LED on
    timer.start();          // start timer
    pc.printf("CAN_Hello board #1\r\n");
#else
    led = OFF;      // turn LED off
    pc.printf("CAN_Hello board #2\r\n");
#endif
    while(1) {
        if(timer.read_ms() >= 2000) {    // check for timeout
            timer.stop();                // stop timer
            timer.reset();               // reset timer
            counter++;                   // increment counter
            voltage = analogIn * 3.3f;   // read the small drift voltage from analog input
            txMsg.clear();               // clear Tx message storage
            txMsg.id = TX_ID;            // set ID
            // append data (total data length must not exceed 8 bytes!)
            txMsg << counter;   // one byte
            txMsg << voltage;   // four bytes
             
            if(can.write(txMsg)) {       // transmit message
                led = OFF;               // turn the LED off
                pc.printf("-------------------------------------\r\n");
                pc.printf("-------------------------------------\r\n");
                pc.printf("CAN message sent\r\n");
                printMsg(txMsg);
                pc.printf("  counter = %d\r\n", counter);
                pc.printf("  voltage = %e V\r\n", voltage);
            }
            else
                pc.printf("Transmission error\r\n");
        }
    }
}