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
Diff: main.cpp
- Revision:
- 5:37ab4112d547
- Parent:
- 4:09d564da0e24
- Child:
- 6:c893b98fc2b5
--- a/main.cpp Wed Apr 25 12:00:10 2018 +0000
+++ b/main.cpp Tue Feb 05 14:51:20 2019 +0000
@@ -19,17 +19,16 @@
*
*/
-//#define TARGET_STM32F103C8T6 1 // uncomment this line and import the mbed-STM32F103C8T6 library when using STM32F103C8T6 boards!
+//#define TARGET_STM32F103C8T6 1 // uncomment this line when using STM32F103C8T6 boards!
#define BOARD1 1 // comment out this line when compiling for board #2
#if defined(TARGET_STM32F103C8T6)
-#include "stm32f103c8t6.h"
-#define LED_PIN PC_13
+#define LED_PIN PC_13
const int OFF = 1;
const int ON = 0;
#else
-#define LED_PIN LED1
+#define LED_PIN LED1
const int OFF = 0;
const int ON = 1;
#endif
@@ -59,7 +58,8 @@
* @param CANMessage to print
* @retval
*/
-void printMsg(CANMessage& msg) {
+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);
@@ -71,6 +71,29 @@
}
/**
+ * @brief Handles received CAN messages
+ * @note Called on CAN msg received interrupt.
+ * @param
+ * @retval
+ */
+void onCanReceived(void)
+{
+ can.read(rxMsg);
+ printMsg(rxMsg);
+
+ if (rxMsg.id == RX_ID) {
+ // extract data from the received CAN message
+ // in the same order as 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
+}
+
+
+/**
* @brief Main
* @note
* @param
@@ -78,11 +101,11 @@
*/
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
+ can.filter(RX_ID, 0xFFF, CANStandard, 0); // set filter #0 to accept only standard messages with ID == RX_ID
+ can.attach(onCanReceived); // attach ISP
+
#if defined(BOARD1)
led = ON; // turn the LED on
timer.start(); // start timer
@@ -96,10 +119,13 @@
timer.stop(); // stop timer
timer.reset(); // reset timer
counter++; // increment counter
- voltage = analogIn * 3.3f; // read the small drifting voltage from analog input
+ voltage = analogIn * 3.3f; // read the small drift 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!)
+ // append data (total data length must not exceed 8 bytes!)
+ txMsg << counter; // one byte
+ txMsg << voltage; // four bytes
+
if(can.write(txMsg)) { // transmit message
led = OFF; // turn the LED off
pc.printf("-------------------------------------\r\n");
@@ -111,20 +137,5 @@
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
- }
- }
}
}