Zoltan Hudak
Using CAN bus with (not just NUCLEO) mbed boards
Using CAN bus with mbed boards
Two low cost STM32F103C8T6 boards are connected to the same CAN bus via transceivers (MCP2551 or TJA1040, or etc.). CAN transceivers are not part of NUCLEO boards, therefore must be added by us. Remember also that CAN bus (even a short one) must be terminated with 120 Ohm resitors at both ends. Although there seems to be an alternative solution.
Schematic
Hookup
The mbed boards in this example are transmitting CAN messages carrying two data items:
uint8_t counter; // one byte float voltage; // four bytes
So in this case the total length of payload data is five bytes (must not exceed eight bytes).
For our convenience, the "<<" (append) operator (defined in CANMsg library) is used to add data to the CAN message.
The usage of "<<" and ">>" operators is similar to the C++ io-streams operators. We can append data one at a time
txMsg << counter; txMsg << voltage;
or combine all into one expression.
txMsg << counter << voltage;
The actual data length of a CAN message is automatically updated when using "<<" or ">>" operators.
After successful transmission the CAN message is printed to the serial terminal of the connected PC. So we can check the details (ID, type, format, length and raw data). If something goes wrong during transmission a "Transmission error" message is printed to the serial terminal.
On arrival of a CAN message it's also printed to the serial terminal of the connected PC. So we can see the details (ID, type, format, length and raw data). Then its ID is checked. If there is a match with the ID of awaited message then data is extracted from the CAN message (in the same sequence as it was appended before transmitting) using the ">>" (extract) operator one at a time
rxMsg >> counter; rxMsg >> voltage;
or all in one shot
rxMsg >> counter >> voltage;
The same source code is used for both boards, but:
- For board #1 compile the example without any change to main.cpp
- For board #2 comment out the line
#define BOARD1 1before compiling
Once binaries have been downloaded to the boards reset both board at the same time.
NOTE:
The code published here was written for the official NUCLEO boards. When using STM32F103C8T6 boards, shown in the picture above (on-board LED is active on 0),
- Include (uncomment) the line
#define TARGET_STM32F103C8T6 1 - Select NUCLEO-F103RB as target platform for the online compiler.
CAN bus related information
main.cpp
- Committer:
- hudakz
- Date:
- 2018-03-29
- Revision:
- 3:87a128bca8f5
- Parent:
- 2:6546e4a2d593
- Child:
- 4:09d564da0e24
File content as of revision 3:87a128bca8f5:
/*
* An example showing how to use the mbed CAN API:
*
* Two affordable (about $2 on ebay) STM32F103C8T6 boards (20kB SRAM, 64kB Flash),
* (see [https://developer.mbed.org/users/hudakz/code/STM32F103C8T6_Hello/] for more details)
* are connected to the same CAN bus via transceivers (MCP2551 or TJA1040, or etc.).
* CAN transceivers are not part of NUCLEO boards, therefore must be added by you.
* Remember also that CAN bus (even a short one) must be terminated with 120 Ohm resitors at both ends.
*
* For more details see the wiki page <https://developer.mbed.org/users/hudakz/code/CAN_Hello/>
*
* NOTE: If you'd like to use an STM32F103C8T6 board uncomment line 23
*
* The same code is used for both mbed boards, but:
* For board #1 compile the example without any change.
* For board #2 comment out line 21 before compiling
*
* Once the binaries have been downloaded to the boards reset both boards at the same time.
*
*/
#define BOARD1 1 // comment out this line when compiling for board #2
//#define TARGET_STM32F103C8T6 1 // uncomment this line when using STM32F103C8T6 boards!
#if defined(TARGET_STM32F103C8T6)
#include "stm32f103c8t6.h"
#define LED_PIN PC_13
const int OFF = 1;
const int ON = 0;
#else
#define LED_PIN LED1
const int OFF = 0;
const int ON = 1;
#endif
#if defined(BOARD1)
const unsigned int RX_ID = 0x100;
const unsigned int TX_ID = 0x101;
#else
const unsigned int RX_ID = 0x101;
const unsigned int TX_ID = 0x100;
#endif
#include "mbed.h"
#include "CANMsg.h"
Serial pc(USBTX, USBRX);
CAN can(p30, p29); // CAN Rx pin name, CAN Tx pin name
CANMsg rxMsg;
CANMsg txMsg;
DigitalOut led(LED_PIN);
Timer timer;
uint8_t counter = 0;
AnalogIn analogIn(A0);
float voltage;
/**
* @brief Prints CAN msg to PC's serial terminal
* @note
* @param CANMessage to print
* @retval
*/
void printMsg(CANMessage& msg) {
pc.printf(" ID = 0x%.3x\r\n", msg.id);
pc.printf(" Type = %d\r\n", msg.type);
pc.printf(" Format = %d\r\n", msg.format);
pc.printf(" Length = %d\r\n", msg.len);
pc.printf(" Data =");
for(int i = 0; i < msg.len; i++)
pc.printf(" 0x%.2X", msg.data[i]);
pc.printf("\r\n");
}
/**
* @brief Main
* @note
* @param
* @retval
*/
int main(void)
{
#if defined(TARGET_STM32F103C8T6)
confSysClock(); //Configure system clock (72MHz HSE clock, 48MHz USB clock)
#endif
pc.baud(9600); // set Serial speed
can.frequency(1000000); // set bit rate to 1Mbps
#if defined(BOARD1)
led = ON; // turn the LED on
timer.start(); // start timer
pc.printf("CAN_Hello board #1\r\n");
#else
led = OFF; // turn LED off
pc.printf("CAN_Hello board #2\r\n");
#endif
while(1) {
if(timer.read_ms() >= 1000) { // check for timeout
timer.stop(); // stop timer
timer.reset(); // reset timer
counter++; // increment counter
voltage = analogIn * 3.3f; // read the small drifting voltage from analog input
txMsg.clear(); // clear Tx message storage
txMsg.id = TX_ID; // set ID
txMsg << counter << voltage; // append data (total data length must not exceed 8 bytes!)
if(can.write(txMsg)) { // transmit message
led = OFF; // turn the LED off
pc.printf("-------------------------------------\r\n");
pc.printf("CAN message sent\r\n");
printMsg(txMsg);
pc.printf(" counter = %d\r\n", counter);
pc.printf(" voltage = %e V\r\n", voltage);
}
else
pc.printf("Transmission error\r\n");
}
if(can.read(rxMsg)) {
led = ON; // turn the LED on
pc.printf("-------------------------------------\r\n");
pc.printf("CAN message received\r\n");
printMsg(rxMsg);
// Filtering performed by software:
if(rxMsg.id == RX_ID) {
rxMsg >> counter >> voltage; // extract data from the received CAN message
pc.printf(" counter = %d\r\n", counter);
pc.printf(" voltage = %e V\r\n", voltage);
timer.start(); // transmission lag
}
}
}
}