if you have a set of map registers, one of which is dedicated to moving the bit-mapped registers then you can move it about by adding the map-register content to the current address of the bitmapped region. That happens transparently to the instructions. You do have to program the thing, though. If you look carefully at the instruction binaries, you'll see how the bit-addressable registers' bits are addressed. Extend that same concept to addressing the SFR's, with an offset from the page registers, i.e. transparently to the user/code, but imposed via the hardware, a different part of the SFR-space is now bit-addressable.

The page registers can be accessed via two locations in SFR-space, one for the address and another for the content, simiarly to the way in which the innards of the HD44780 is addressed. The concept can be implemented in a way that's infinitely extensible, so anything's possible with this approach. There can be an offset register for each bit, just as there can be an offset register for each page of memory, either code or data. It's all up to the designer/implementor.

It would be up to the programmer to keep track of the effect of his modification of the page table(s).

That way, the entire mess can be kept instruction-set compatible.

RE