CAN bus without transceivers
According to Siemens application note AP2921 On-Board Communication via CAN without Transceivers all Rx and Tx lines shall be connected to a single data line pulled up to VCC. Though Tx outputs shall be connected through fast diodes rather than directly to avoid short circuits at the output pins. Such simplified circuitry is suitable when CAN devices are located close to each other, for exapmle on the same card or in the same rack.
Make sure that +3.3V is used as pull up voltage with MBED boards (rather than +5V)!
It is also very important that the current at one port pin does not exceed 1.6 mA.
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