==V9990==
The V9990 E-VDP-III or 'Graphics 9000' is a Video Display Processor (VDP) by Yamaha which is based on an unreleased VDP (V9978) that was intended for the unreleased MSX3.
This chip is available on graphics cards for the MSX and CPC.
==Technical==
The official PDF
* In the following "databus" means that the v9990 doesn't assert the bus, it doesn't provide data, so the value read is "floating-bus" or the value on the z80 databus at the time. More commonly on CPC it's &ff, but there are some configurations of CPC where this differs.