RS-485 with Modbus vs CAN Bus

[Red_Micro]

At a high level I know some of the advantages/disadvantages and differences of both RS485-Modbus and CAN Bus. In this post I just would like to read opinions based on people's experiences. Under which conditions or application you would choose a protocol over the other?

[H.O]

Having used MODBUS RTU a bit but never CAN I won't call myself an expert but I know that CAN is a multimaster protocol and MODBUS RTU (or ASCII for that matter) is not which means MODBUS would be out if the application wasn't suitable for the master-slave type aproach that MODBUS uses.

[max_torque]

The significant diffence is that CAN includes message collision avoidance and prioritisation/arbitration at a HARDWARE level.  RS-485 does neither, so it is up to a Master device to schedule the bus timing and loading, whereas with CAN no master is required, and each device on the bus is able to simply transmit it's message at any time (although it is up to the bus architect to ensure that there is sufficient spare capacity on the bus, using suitable message prriorities to ensure that all devices get their fair share)

[Renate]

Single master, use Modbus. Any µC with a UART can do it.

Multiple masters/asynchronous alarms, use CAN. You'd probably want to use a CAN chip.