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 1
before 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
Diff: main.cpp
- Revision:
- 8:c65afde7f7f5
- Parent:
- 7:883da97339ab
- Child:
- 9:3211e88e30a5
--- a/main.cpp Tue Feb 05 15:01:00 2019 +0000 +++ b/main.cpp Tue Feb 05 19:03:26 2019 +0000 @@ -7,9 +7,6 @@ * 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: When using an STM32F103C8T6 board uncomment line 22 and import the mbed-STM32F103C8T6 library * * The same code is used for both mbed boards, but: * For board #1 compile the example without any change. @@ -19,7 +16,7 @@ * */ -//#define TARGET_STM32F103C8T6 1 // uncomment this line when using STM32F103C8T6 boards! +//#define TARGET_STM32F103C8T6 1 // uncomment this line to use STM32F103C8T6 boards #define BOARD1 1 // comment out this line when compiling for board #2 @@ -57,7 +54,7 @@ float voltage; /** - * @brief Prints CAN msg to PC's serial terminal + * @brief Prints CAN message to PC's serial terminal * @note * @param CANMessage to print * @retval @@ -76,7 +73,7 @@ /** * @brief Handles received CAN messages - * @note Called on CAN msg received interrupt. + * @note Called on 'CAN message received' interrupt. * @param * @retval */ @@ -87,13 +84,13 @@ if (rxMsg.id == RX_ID) { // extract data from the received CAN message - // in the same order as was added on the transmitter side + // in the same order as it was added on the transmitter side rxMsg >> counter; rxMsg >> voltage; pc.printf(" counter = %d\r\n", counter); pc.printf(" voltage = %e V\r\n", voltage); } - timer.start(); // to transmit next message + timer.start(); // to transmit next message in main } @@ -105,10 +102,10 @@ */ int main(void) { - pc.baud(9600); // set Serial speed - can.frequency(1000000); // set bit rate to 1Mbps + pc.baud(9600); // set serial speed + can.frequency(1000000); // set CAN bit rate to 1Mbps can.filter(RX_ID, 0xFFF, CANStandard, 0); // set filter #0 to accept only standard messages with ID == RX_ID - can.attach(onCanReceived); // attach ISP + can.attach(onCanReceived); // attach ISR to handle received messages #if defined(BOARD1) led = ON; // turn the LED on