CAN-BUS Shield

Introduction

CAN-BUS is a common industrial bus because of its long travel distance, medium communication speed and high reliability. It is commonly found on modern machine tools and as an automotive diagnostic bus. This CAN-BUS Shield adopts MCP2515 CAN Bus controller with SPI interface and MCP2551 CAN transceiver to give your Arduino/Seeeduino CAN-BUS capibility. With an OBD-II converter cable added on and the OBD-II library imported, you are ready to build an onboard diagnostic device or data logger.

Features

• Implements CAN V2.0B at up to 1 Mb/s
• SPI Interface up to 10 MHz
• Standard (11 bit) and extended (29 bit) data and remote frames
• Two receive buffers with prioritized message storage
• Industrial standard 9 pin sub-D connector
• Two LED indicators

Application Ideas

• CAN communication network
• Industrial monitor system
• Onboard diagnostic tool & data logger

Specifications

Item	Min	Typical	Max	Uint
Voltage	4.8	5.0	5.2	VDC
Dimensions	68x53			mm
Net Weight	50			g

Interface Function

Usage

Here we provide a demo to show you how to build up communication between two CAN-BUS node.

Hardware Installation

We use two CAN-BUS shields here, one as a transmitter and the other as a receiver. Install the hardware like the picture below. Connect two CAN-BUS terminals on boards with jumper wires. Make sure the left terminal gets connected to the left on the other board, also the right terminal.

Now plug two microcontrollers to your computer, let's move on to the software part.

Software Installation

1. Download the CAN-BUS Source code file for Arduino 1.0 and release it in the libraries file in the Arduino-1.0 program.: ..\arduino-1.0\libraries.

2. Open the Arduino-1.0, and you will find two examples: "receive" and "send". Open both of them, you should get two programming windows now.

3. Upload two examples to two boards separately. Choose the board via the path: Tools -->Serial Port-->COMX. Note down which board is assigned as a "send" node and which board is assigned as a "receive" node.

4. Open the "Serial Monitor" on the "receive" COM, you will get message sent from the "send" node. Here we have the preset message "0 1 2 3 4 5 6 7" showing in the following picture.

Function Explanation

1. Set the BaudRate

This function is used to initialize the baudrate of the CAN Bus system.

The available baudrates are listed as follws:

CAN_5KBPS, CAN_10KBPS, CAN_20KBPS, CAN_40KBPS, CAN_50KBPS, CAN_80KBPS, CAN_100KBPS, CAN_125KBPS, CAN_200KBPS, CAN_250KBPS and CAN_500KBPS.

2. Set Receive Mask and Filter

There are 2 receive mask registers and 5 filter registers on the controller chip that guarantee you get data from the target device. They are useful especially in a large network consisting of numerous nodes.

We provide two functions for you to utilize these mask and filter registers. They are:

init_Mask(unsigned char num, unsigned char ext, unsigned char ulData); & init_Filt(unsigned char num, unsigned char ext, unsigned char ulData);

"num" represents which register to use. You can fill 0 or 1 for mask and 0 to 5 for filter.

"ext" represents the status of the frame. 0 means it's a mask or filter for a standard frame. 1 means it's for a extended frame.

"ulData" represents the content of the mask of filter.

3. Check Receive

The MCP2515 can operate in either a polled mode, where the software checks for a received frame, or using additional pins to signal that a frame has been received or transmit completed. Use the following function to poll for received frames.

INT8U MCP_CAN::checkReceive(void);

The function will return 1 if a frame arrives, and 0 if nothing arrives.

4. Get CAN ID

When some data arrive, you can use the following function to get the CAN ID of the "send" node.

INT32U MCP_CAN::getCanId(void)

5. Send Data

CAN.sendMsgBuf(INT8U id, INT8U ext, INT8U len, data_buf);

is a function to send data onto the bus. In which:

"id" represents where the data come from.

"ext" represents the status of the frame. '0' means standard frame. '1' means extended frame.

"len" represents the length of this frame.

"data_buf" is the content of this message.

For example, In the 'send' example, we have:

  
unsigned char stmp[8] = {0, 1, 2, 3, 4, 5, 6, 7};

CAN.sendMsgBuf(0x00, 0, 8, stmp); //send out the message 'stmp' to the bus and tell other devices this is a standard frame from 0x00.

6. Receive Data

The following function is used to receive data on the 'receive' node:

CAN.readMsgBuf(unsigned char len, unsigned char buf);

In conditions that masks and filters have been set. This function can only get frames that meet the requirements of masks and filters.

"len" represents the data length.

"buf" is where you store the data.

Support

Ask questions on Seeed forum.

Resources

• CAN-BUS Shield Schematic.pdf
• CAN-BUS Shield eagle file
• CAN-BUS Source code file for Arduino 1.0
• MCP2515 datasheet
• MCP2551 datasheet
  

Licensing

This documentation is licensed under the Creative Commons Attribution-ShareAlike License 3.0 Source code and libraries are licensed under GPL/LGPL, see source code files for details.