CAN BUS SHEILD AND UNO R3 ISSUE

Projects Networking, Protocols, and Devices
1

I am trying to use this code with a Seeeduino Can Bus Shield and a Arduino R3. I am using this library CAN_BUS_Shield/CAN_BUS_Shield at master · yexiaobo-seeedstudio/CAN_BUS_Shield · GitHub. the send.ino

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

void setup()
{
  // init can bus, baudrate: 100k
  CAN.begin(CAN_125KBPS);
  
}

unsigned char stmp[8] = {0x10, 0x00, 0x20, 0x00,0x0 0,0x0 0, 0x00, 0x00};
void loop()
{
  // send data:  id = 0x430, standard flame, data length = 8, stmp: data buf
  CAN.sendMsgBuf(0x430, 0, 8, stmp);  
  delay(1000);                       // send data per 1000ms
}

I tried hooking this up to a bench setup with a vehicle amplifier, display, and a switch bank. I am also running Vector Canoe and simulating some other in vehicle messages. I am using canoe to read the bus messages on the Can bus. I have the correct baud rate and correct id and dlc. When I run the setup I can see all the messages from my hardware and the simulated canoe messages but as soon as I hook up the Can shield w/ Arduino I get error frames from those components. I then unhooked the can lines and read the signal with an Oscope. The CAN signal looked good(sorry no photo right now). I then changed the code to delay for 5 seconds in between message send commands and noticed there is a constant signal coming out of the CANH and CANL ports. It does this with CAN lines not connected to anything and with CAN lines connected in circuit. I am not a very good programmer so I dont where to start with figuring out if this is a software issue or a hardware issue. Any guidance would be greatly appreciated.

2

I then changed the code to delay for 5 seconds in between message send commands and noticed there is a constant signal coming out of the CANH and CANL ports.

How does this signal look like? Rectangular or sinusoid wave?

3

It is a square wave. It looks like good CAN bus signal. I did a direct comparison with signal on a known good can bus (one that is working). They are very familiar. One thing I did was I did some research last night and found that the CAN-Bus shield comes with a termination resistor populated on the board. I removed the resistor and no change. I then added a 120 ohm resistor and still no change constant signal coming from the outputs. I will try to upload a picture of the signal I am getting later.

4

This is the description of "normal mode" in the datasheet:

Normal mode is the standard operating mode of the
MCP2515. In this mode, the device actively monitors all
bus messages and generates acknowledge bits, error
frames, etc. This is also the only mode in which the
MCP2515 will transmit messages over the CAN bus.

After initialization the library set the chip into this mode. So I'd guess that without a connection the chips is generating error frames because it doesn't get correct readings.

5

Try the library on my github: GitHub - coryjfowler/MCP_CAN_lib: MCP_CAN Library

I found some bugs in the Seeed library back in October dealing with extended identifiers, then I tested the baud rates against a Peak PCAN-USB dongle and found some errors in the baud multipliers that I also fixed. I hope this helps you.