AC 800M is a PLC or a DCS? or whats the difference technically
This is an old question and there is no clear answer. In your case, the best answer is "The AC800M controller is both"
You can use the AC800M as a standalone controller on a plant like a boiler with a single panel and program it just like a PLC.
You can use several AC800M controllers with distributed software, and multiple operator workstations across multiple power plants in different locations and program it just like a DCS.
Or you can do pretty much anything in between.
I think PLC or DCS - in our days that is difficult to say. That was definition about 15-20 years ago. What functionality do you look for in order to clacify the controllers for one of these?
For example - normally PLC's have a possibility for freeweeling cycle time (not fixedcycle time). AC800M has no free-weeling cycle (task) - it is all the time fixed time.