Eduardo Pino

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7 years, 1 month ago.

Concatenate 2 bytes from a CANMessage

Hey folks

I am currently working on a project where I am trying to communicate with a device via CAN using an Nucleo-F767Zi board and mbed CAN library.

The problem I am facing is that one of the parameters that this device is sending is divided in 2 bytes, how can I concatenate this two bytes?

I tried shifting 8 bits and using bitwise OR but it did not work.

Thanks!

2 Answers

Andy A
7 years, 1 month ago.

If you don't want to add an extra library then it should be as simple as:

uint16_t value;
CANMessage dataRx;

main() {
  if(can.read(dataRx)) {
    value = dataRx.data[0] | ((uint16_t)dataRx.data[1] << 8);
     }
}

My guess is that your code didn't work because you shifted the data without first casting it to something larger than 8 bits. value = dataRx.data[0] + dataRx.data[1] * 256; should also work fine.

Accepted Answer
Zoltan Hudak
7 years, 1 month ago.

Hello,
If the parameter is of a known data type then you can try to use the ">>" (extract) operator defined in the CANMsg library.
Let's assume your parameter is of uint16_t type and it's the only data carried by the CANMessage. Then you can extract it from the CAN message as follows:

#include "mbed.h"
#include "CANMsg.h"

uint16_t  parameter;  // your two bytes long parameter
CANMsg    rxMsg;      // storage for the received CAN message

main() {
...

    if(can.read(rxMsg)) {
        ...
        rxMsg >> parameter;  // extracts the parameter from the CAN message and casts it into uint16_t
    }
    ...

}

Have a look also at the CAN_Hello demo.