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.
=== Kanji ROM ===
Testing is limited because the powergraph doesn't have a Kanji ROM.