A further clarification after re-reading your email.
The dongle is the Lawicel CAN232 device. It is simply an RS232 to CAN adapter and is not capable of generating any CAN traffic on its own.
The CDNC software when configured to do so will tell the CAN232 what packet content to send over the CAN bus and when.
So, the way to think about this is there is no traffic/hearbeat unless the CDNC software is generating it.
Set the heartbeat rate and then enable the hearbeat in CDNC and you should have traffic preventing Watchdog resets.
This help clarifiy?
Regards, Stephen --