"Half" bus speed with Arduino UNO and MCP2515

Projects Networking, Protocols, and Devices
1

Hello
I work on a project with Can bus. I use an Arduino UNO and MCP2515. The bus is running, but the bus speed does not fit. If I select 500kbits/s the data comes only with 250kBits/s. Both when sending and/or receiving.

This effect I have with different libraries for MCP2515 as "CAN_Library-master" or "MCP_CAN_lib-master" and it is always the factor 2.

Did someone give me a tip?
Many Thanks

2

Do you use a breakout board for the MCP2515? If yes, please provide a link to it. If not, please post the schemata of how you wired everything. The MCP2515 need and external clock source. This may either be crystal or a clock signal generated by some other source (p.e. the Arduino).

3

Enclosed is an overview of my breadboard with the MCP2515 module.
This setup I have 2 times – also 2 times with the identical effect.

In this example, only one setup communicates with a Peak dongle. The Peak dongle sends every second a message, received by the MCP2515 and send back.

In this case I work with the MCP_CAN_lib

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

MCP_CAN CAN0(10); // Set CS to pin 10

unsigned int MsgCounter = 0;
unsigned long currentMillis;

void setup() {

Serial.begin(9600);

// Initialize MCP2515 running at 16MHz with a baudrate of 500kb/s and the masks and filters disabled.
if(CAN0.begin(MCP_ANY, CAN_500KBPS, MCP_16MHZ) == CAN_OK) Serial.println("MCP2515 Initialized Successfully!");
else Serial.println("Error Initializing MCP2515...");

CAN0.setMode(MCP_NORMAL); // Change to normal mode to allow messages to be transmitted
}

void loop() {
long unsigned int rxId;
unsigned char len = 0;
unsigned char rxBuf[8];

while (CAN_MSGAVAIL == CAN0.checkReceive())
{
CAN0.readMsgBuf(&rxId, &len, rxBuf); // Read data
CAN0.sendMsgBuf(rxId+1, 0, len, rxBuf); // and send echo back

currentMillis = millis();
MsgCounter++;
Serial.print(MsgCounter);
Serial.print(" ");
Serial.println(currentMillis);
}
}

Also a screenshot of the Pcan-View with the bus speed. It is only 250kbit/s and not 500 as defined in the programm. The same result I also get with my CANalyzer tool.

If a message is received, I output a time stamp on the serial interface. The difference time is 1000msek as from the peak dongle.

Do you have any idea?

Regards
Bjoern

breadboard.jpg
breadboard.jpg729×476 47.1 KB

PCan-View.jpg
PCan-View.jpg732×360 46.1 KB

ComOutput.jpg

4

Whats the crystal speed on your CAN modules MCP2515? Also, how are you measuring speed? Timming between bits on the scope?

5 
if(CAN0.begin(MCP_ANY, CAN_500KBPS, MCP_16MHZ) == CAN_OK) Serial.println("MCP2515 Initialized Successfully!");

Why are you telling the MCP it runs on 16MHz when the crystal is a 8MHz (at least that's on the picture you sent, you STILL didn't provide a link to that breakout board!)

6

All the NiRen boards I've received are fitted with an 8 MHz crystal.

7

Ups. Your are right
Thank you guys :grinning:

I was just in tunnel mode and did not think of the module
Now I understand why. That was important to me

Thank you and til nextime