A few more tidbits from the Servicehandbuch:

F000H Either 8KB Chargen or 32KB framebuffer, determined by
F9A0H transferring 1 or 0 here switches (F940 according to another page)

F9B0H/F9B2H 8041 on graphics card, responsible for Mouse and Screen invert (maybe cross-check negativ.com/positiv.com?)

F980H-F9BFH graphics card I/O
F980H-F9E0H select signals for 2674 graphics chip

FB01H graphics card control, if EXTRDY-N is low, the graphcis card is present

p.162 of the Servicehandbuch seems to suggest that the system can alternate between RAM and VRAM access between F0000H and F7000H without disturbing the screen.

The keyboard contains an 8035 (romless 8048) that talks to one of the 2661's using 600 baud, no parity, 1 start/stop bit

NCR DMV- DEC Rainbow- Siemens PCD- ITT 3030-Oly People- Acorn A5000- Olivetti M20