9 years, 10 months ago.

Need help with CAN Bus code

Hello. I have tried several of the mbed CAN Bus examples without success. I simply want to send a byte from the CAN transmitter. The byte comes from a counter in the loop that should send a new CAN message every 300 msec. (I printed info to TeraTerm to test the code and commented out the printf statements for a real run. See sample at the end of this post.)

Here's the simple code I created:

#include "mbed.h"
 
DigitalOut led2(LED2);
DigitalOut led4(LED4);
CAN can1(p30, p29); //CAN Transmitter
char counter = 0;
Serial pc(USBTX, USBRX); // tx, rx

int main()
{
    pc.baud(9600);
    can1.frequency(125000);
    can1.reset();
    
    while(1)
    {
        //pc.printf("In while loop\n\r");
        led2 = !led2; 
        wait(0.3);
        //pc.printf("Sending\n\r");
        if (can1.write(CANMessage(0x139, &counter, 1)))
            {
               led2 = !led2; 
               //pc.printf("Message sent: %d\n\r", counter);
               counter++;
            }
        else
            {
                led4 = !led4;
            }                   
    }
}

I do see a burst of pulses every 300 msec, but they look nothing like a CAN message. I see a long logic-0 pulse followed by 15 shorter logic-0 pulses in each "message." My logic-analyzer bit rate and the bit rate in the code match. I can see the same signals on a scope. I've also included the terminal output that shows what the program produces when I use the print statements, so I know the counter increments, although I don't see CAN messages.

I'm lost at this point and would appreciate help. Thanks.

Message sent: 30

In while loop

Sending

Message sent: 31

In while loop

Sending

Message sent: 3 2 In while loop

Sending

etc...