True RS485 4-wire full duplex

In all of the years I've been in this industry I've never come across equipment that had true RS485 4-wire full duplex as a communications option (not to be confused with RS422 4-wire full duplex). What kind of equipment has anyone else come across over the years with it as the communications method?

P.S. I'm not saying that there isn't anything and in fact it could be a lot more prevalent that I'm aware of (which is why I ask the question).

No, but I have only been involved with Modbus, which by its poll/response nature is almost always implemented as a half duplex protocol. I suspect that the reason is that the protocol implementation on the field devices is an after-the-fact design with not-very-powerful processors, as evidenced by more than a couple which choke on polls faster than 1 second, sometimes 2 seconds.



What's the benefit of full duplex when a slave could 'see' another polling message before the slave has even finished its reply? Choke, choke.



Ron Hulsebos (Hulsebus?) created a list of hundreds of industrial protocols about 15 years ago and I could name 7 that were not on his list, so I suspect that someone somewhere has used RS-485 full duplex but I don't who.

Mitsubishi servo MR J A and FX5 on 115k Modbus - works flawlessly.