Ring configurations... a few more points.

To implement rings in 485/422 you'd need to transceivers since the differential pairs are bi directional and have no separate tx and rx signals. In this configuration you can a bidirectional ring.

This means the protocol can run various ways, most previously mentioned. Adding a little more now, you can do the following if you take care in your ring communications drivers.

Ring configuration protocols can include a direction and distance to node discovery for finding the primary/secondary path to each node to which it needs to communicate. The the second path (direction) can be used for load balancing or when the ring network identifies a cut or dead node.

Ring networks with subrings are interesting structures with some surprising efficiencies but you shouldn't attempt this lightly. You must be a master at buffers and interrupt port to port routing and for familiarity with automata theory can probably speed up you routing and handoff routines.

For RS485/422 you should not use rings when the system is not expected to be running ALL THE TIME. These drivers are not pass-through drivers that isolate a node when powered down.

In 1982 I did some work on such a LAN for a company that sold critical and reliable hospital data communications system. Our primary ring nodes all had redundant Multi-Bus systems that isolated the node if the system powered down, failed to communicate or triggered a "chatter timer" (ie if it talked too much as in a lockup or bug that exceeded the maximum TX window).

We had redundant LAN cards a failure identification LEDs for quick replacement identification.

I designed the board called the "Master Data Tap" and if you says that many times quickly, you'll figure out what it became known as. This was the board that decoded the datastream and passed it on to the subnet's processor, made all the decisions whether the node was valid and isolated and switched to backup if protocol violations were detected and a backup was sensed as installed. You probably think this was a job for a microprocessor but in fact it was done with 17 logic gates and flip-flops. I keep one of the old boards on the wall in my office. :)

It was a lot fun.

aka J