This was standard on the PC-Engine, and I think the majority of VDC type display controllers of the time.. Personally, I’d take a bank switching scheme whereby

This was standard on the PC-Engine, and I think the majority of VDC type display controllers of the time.. Personally, I’d take a bank switching scheme whereby CPU reads come from RAM as standard and CPU writes go to graphics memory.. Even as simple as 1 bit mapping of writes to either CPU RAM or VDC RAM would suffice well.. Though more complex is possible..