What you’re quoting is:
And I don’t think you’re correctly interpreting what this is saying.
This is “USB to CAN bus bridge mode” - the Main Controller Board is acting as the USB to CAN interface and there is only one path for the control signals. In my opinion, it is the simpler, cheaper and more elegant method of connecting a CAN toolhead.
A “USB to CAN bus” interface is a separate piece of hardware (usually referred to as a “U2C” interface/device) that introduces a second USB bus path and adds to the volume and complexity of communications throughout the printer.
When I said “complexity”, as well as the need for supporting firmware, power and wiring on a separate device, I’m also referring to the strange way the U2C board shown above is wired - we had quite a discussion some time ago about how the U2C board above is actually wired and why (I understand how it is wired but I have no idea why). If you’re thinking of going this route, I highly recommend only using a Canable 2 board without the extra connectors.
Yes, I know that in my diagram above I have marked the lower “USB Cable” going to the USB A connectors on the card which don’t actually connect to USB signals - I did this to keep the diagram simple.
To net things out, I’ve controlled CAN devices both ways in printers and I’ve never experienced a problem. For the past few years, I’ve only run “USB to CAN bus bridge mode” because it is simpler and adding a U2C device adds its own cost and complexity to the system as discussed above.
I’m not really sure of the history behind the manual page saying there can be a problem - I suspect that some people have experienced “Timer Too Close” errors when running with a U2C device that went away when they ran their main controller board in USB to CAN bus bridge mode.
In my experience, CAN works well and is very reliable, regardless of how it is implemented.