The 80286 2nd processor was never commercially released, and is only found in a few examples of the ABC 310 that exist. What we know is that it used the same boot ROMs that were found in the later Master 512, and had 1MB RAM. All photos out there seem to be of the same board and no schematics have been found so a little reverse engineering of the boot code was required. The boot ROM detects whether it is running on 80186 or 80286 and acts differently accordingly.
There is no known software specifically developed for the ABC 310 so am running the Master 512 System disk which shows it running on the 80286 and behaves differently from the Master in my previous post.
I've seen some suggestions that the ABC 310 was intended to run Concurrent DOS, which might have been able to use protected mode.
While DOS Plus contains two sets of Tube client code (for the 186 and 286), the 286 code is buggy for type 2 / 3 memory transfers initiated by the host. The transfer address is in the data segment, but the transfer code accesses the corresponding address in the code segment.