CANbus simplest circuit for a start

[atferrari]

When I was about to implement a node, the chance I had to get access to a running CANbus network, failed.

In spite I saw this not reccomended, what could be the simplest implementation (two nodes) to start experimenting?

a) Basically, could anyone tell me what should be the simplest settings to have more chances to get them up and running. The most basic the better, I think.

b) I presume that handling errors is capital here. Since I expect lot of them, can you suggest what is the best way to handle them? I fear to find the info, a bit on the overwhelming side.

I will use the 18F4585, a (TI or Microchip) transceiver,. LCD display, buttons and LEds.

 

[Papabravo]

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.

 

[atferrari]

Hola P B,

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

Thanks for that!

Hope to post a good outcome soon.

 

[Papabravo]

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.