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CAN or Controller-area Network is a bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
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Exporting to offline toolchains 
#include "mbed.h"
Ticker ticker;
DigitalOut led1(LED1);
DigitalOut led2(LED2);
CAN can1(p9, p10);
CAN can2(p30, p29);
char counter = 0;
void send() {
printf("send()\n");
if(can1.write(CANMessage(1337, &counter, 1))) {
printf("wloop()\n");
counter++;
printf("Message sent: %d\n", counter);
}
led1 = !led1;
}
int main() {
printf("main()\n");
ticker.attach(&send, 1);
CANMessage msg;
while(1) {
printf("loop()\n");
if(can2.read(msg)) {
printf("Message received: %d\n", msg.data[0]);
led2 = !led2;
}
wait(0.2);
}
}
This example sends from one CAN bus (can1) an counter while it is listen on the other CAN bus (can2) to receive a packet. Each bus controller should be connected to a CAN bus transceiver. These should be connected together at a CAN bus.
API summary
| CANMessage | |
| Functions | |
| CANMessage | Creates empty CAN message. |
| CANMessage | Creates CAN message with specific content. |
| CANMessage | Creates CAN remote message. |
| Variables | |
| id | The message id. |
| data | Space for 8 byte payload. |
| len | Length of data in bytes. |
| format | Defines if the message has standard or extended format. |
| type | Defines the type of a message. |
| CAN | A can bus client, used for communicating with can devices |
| Functions | |
| CAN | Creates an CAN interface connected to specific pins. |
| frequency | Set the frequency of the CAN interface |
| write | Write a CANMessage to the bus. |
| read | Read a CANMessage from the bus. |
| reset | Reset CAN interface. |
| monitor | Puts or removes the CAN interface into silent monitoring mode |
| rderror | Returns number of read errors to detect read overflow errors. |
| tderror | Returns number of write errors to detect write overflow errors. |
| attach | Attach a function to call whenever a CAN frame received interrupt is generated. |
class CANMessage : public CAN_Message
Creates empty CAN message.
CANMessage()
The message id.
unsigned int id
Space for 8 byte payload.
unsigned char data[8]
Length of data in bytes.
unsigned char len
Defines if the message has standard or extended format.
CANFormat format
Defines the type of a message.
CANType type
A can bus client, used for communicating with can devices
class CAN : public Base
Creates an CAN interface connected to specific pins.
CAN( PinName rd, PinName td )
Set the frequency of the CAN interface
int frequency( int hz )
Write a CANMessage to the bus.
int write( CANMessage msg )
Read a CANMessage from the bus.
int read( CANMessage & msg )
Reset CAN interface.
void reset()
Puts or removes the CAN interface into silent monitoring mode
void monitor( bool silent )
Returns number of read errors to detect read overflow errors.
unsigned char rderror()
Returns number of write errors to detect write overflow errors.
unsigned char tderror()
Attach a function to call whenever a CAN frame received interrupt is generated.
void attach( void (*fptr)(void) )
The CAN Interface can be used on mbed pins p9/p10 and p30/p29
The CAN Interface can be used to write data words out of a CAN port and will return the data received from another CAN device. The CAN clock frequency can be configured.
dedo T wrote: yes, there is a spec for CAN V2.0B: http://www.hehlhans.de/bilder/autos/cdi270/comand/can2spec.pdf The polynome is discribed at Part A - page 13
But you do not need to know this! This polynome is calculated from the CAN-HW-Controller, and, if the crc is wrong on the transmission of a can frame, the HW will automaticaly repeat the can frame again, to enshure, that it will be transmitted correctly. All this stuf is done by the CAN-HW, and you need not think about it on sw side. This is the benefit from a can controller.
I just read up on your reply on changing a CAN CRC, it turns out that the mbed has the CRC hard coded and it can't be modified. The only way is to get an external Controller and communicate to it over SPI.
Lame...
David Smart wrote: Could someone build, test, and confirm the minimal CAN sample is working for them?
Have you seen this page with a minimal setup including transceiver or did you mean that with "confirm the minimal CAN sample" *confused* ? http://mbed.org/projects/cookbook/wiki/CanBusExample1
Hakam abubaha wrote: What is the default frequency? how it can be changed?
Hakam,
I measure a default bit time as 10 μs. That would make the default frequency 100 kHz.
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I'm glad so there is one more CAN in mbed, but you could repair that picture :) http://mbed.org/media/uploads/simon/mbedmicrocontrollerpinout4.png There is drawn only one CAN