CANbus simplest circuit for a start

The simplest system is a lonely node that can hear itself transmitting but with no other node to generate a dominat bit in the ACK slot it retries the message for ever. You can use this lonely node to check the bit timing parameters.

When you have two nodes that look the same on the scope you can put them together to see if they talk.

As for errors there is really nothing to do. It is all handled in the CAN silicon.

Hola P B,

Good idea! Didn't consider the loopback mode...!

Thanks for that!

Hope to post a good outcome soon.

The easiest way to do loopback is to connect a transceiver (PCA82C251) to the CAN Transmit and receive lines. On the CAN Bus side connect a 62 OHm resistor across CAN_H and CAN_L.

Why 62 Ohms you ask. Well the characteristic impedance of a twisted pair is about 120 Ohms. So a long cable terminated at each end is 120 in parallel with 120 or 60 Ohms.