use of arduino with can bus sheild

Question

I'm trying to get VGM CAN message out of a Reachstacker 42-45 tonnes

where I am using an arduino MEGA 2560 with a CAN-BUS shield

this my current code:

#include <SPI.h>
#include "mcp_can.h"


// the cs pin of the version after v1.1 is default to D9
// v0.9b and v1.0 is default D10
const int SPI_CS_PIN = 9;

MCP_CAN CAN(SPI_CS_PIN);                                    // Set CS pin

void setup()
{
    Serial.begin(115200);

START_INIT:

    if(CAN_OK == CAN.begin(CAN_500KBPS))                   // init can bus : baudrate = 500k
    {
        Serial.println("CAN BUS Shield init ok!");
    }
    else
    {
        Serial.println("CAN BUS Shield init fail");
        Serial.println("Init CAN BUS Shield again");
        delay(100);
        goto START_INIT;
    }
}


void loop()
{
    unsigned char len = 0;
    unsigned char buf[8];

    if(CAN_MSGAVAIL == CAN.checkReceive())            // check if data coming
    {
        CAN.readMsgBuf(&len, buf);    // read data,  len: data length, buf: data buf

        unsigned char canId = CAN.getCanId();

        Serial.println("-----------------------------");
        Serial.println("get data from ID: ");
        Serial.println(canId);

        for(int i = 0; i<len; i++)    // print the data
        {
            Serial.print(buf[i]);
            Serial.print("\t");
        }
        Serial.println();
    }
}

this was the result at the time of doing the test, the problem that I do not understand the result

according to the documentation should have a result like this :

this is another part of the documentation :

If someone needs more information or does not understand what I'm looking for, you can request what you need to help me

---

Send data:

// demo: CAN-BUS Shield, send data
#include <mcp_can.h>
#include <SPI.h>

// the cs pin of the version after v1.1 is default to D9
// v0.9b and v1.0 is default D10
const int SPI_CS_PIN = 9;

MCP_CAN CAN(SPI_CS_PIN);                                    // Set CS pin

void setup()
{
    Serial.begin(115200);

START_INIT:

    if(CAN_OK == CAN.begin(CAN_500KBPS))                   // init can bus : baudrate = 500k
    {
        Serial.println("CAN BUS Shield init ok!");
    }
    else
    {
        Serial.println("CAN BUS Shield init fail");
        Serial.println("Init CAN BUS Shield again");
        delay(100);
        goto START_INIT;
    }
}

unsigned char stmp[8] = {0, 1, 2, 3, 4, 5, 6, 7};
void loop()
{
    // send data:  id = 0x00, standrad frame, data len = 8, stmp: data buf
    CAN.sendMsgBuf(0x00, 0, 8, stmp);
    delay(100);                       // send data per 100ms
}

Answer 1

You have two pieces that do not fit between your documentation and the output you are generating:

1. The data payload
2. The ID of the CAN frames

For the data payload it is simply a matter of formatting. You print each byte as integer value, whereas in the documentation it is printed as hexadecimal values. Use

Serial.print(buf[i], HEX)

to get the payload printed as hexadecimal characters.

For the ID of the CAN frames, you see from the documentation that they do not fit inside an unsigned char, as already mentioned in the comment by @Guille. Actually those are 29-bit identifiers, which you should ideally store in an appropriately sized variable. Ideally use an unsigned long:

unsigned long canId = CAN.getCanId();

In the documentation the CAN ID is also printed in hexadecimal, so also here use:

Serial.println(canId, HEX);