Zoltan Hudak / Mbed 2 deprecated CAN_Hello

Using CAN bus with (not just NUCLEO) mbed boards

Dependencies:   mbed CANMsg

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

Zoom in

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.

CAN bus related information

• CAN - Getting Started
• Handbook
• CANopen

--- a/main.cpp	Thu Mar 29 18:57:18 2018 +0000
+++ b/main.cpp	Wed Apr 25 12:00:10 2018 +0000
@@ -9,7 +9,7 @@
  *
  * 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
+ * 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.
@@ -18,9 +18,10 @@
  * 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!
+//#define TARGET_STM32F103C8T6    1       // uncomment this line and import the mbed-STM32F103C8T6 library when using STM32F103C8T6 boards!
+
+#define BOARD1                  1       // comment out this line when compiling for board #2
 
 #if defined(TARGET_STM32F103C8T6)
 #include "stm32f103c8t6.h"
@@ -43,7 +44,7 @@
 #include "CANMsg.h"
 
 Serial              pc(USBTX, USBRX);
-CAN                 can(p30, p29);  // CAN Rx pin name, CAN Tx pin name
+CAN                 can(PB_8, PB_9);  // CAN Rx pin name, CAN Tx pin name
 CANMsg              rxMsg;
 CANMsg              txMsg;
 DigitalOut          led(LED_PIN);