ok forget it. I noob read the addresses wrong. back to the drawing board.
Interesting, hit9918, please keep sharing with us your advances 
That is a good idea, mars, thanks.
The idea is to make it work on a msx2, but offcourse first I will try to make it work on turbo-r.
Anyway, even if I manage to make it work on openmsx, the problem will be to make it work on a real msx.
I flashed the rom on a flashable cartridge and the results are the same: a whole bunch of nothing.
This will not be easy, I see...
Thank you for your help! I very much appreciate it
ok I got a demo that sorts out charset and nametable in plain BASIC.
frustrating hours because one doesn't know.
done that, it is all the same patterns again as known from 9958.
the 9990 has much more, but not in lots bells and whistles, but in one big mechanism.
edit: sprites added. a whole screen wide, ok? 
their patterns are same location as charset of top layer.
1 out &h6f,0 'init superimpose 10 for i = 0 to 23 : read a 12 out (&h64),128+i 'register write mode: 128 + register number 14 out (&h63),a 16 next 60 for i = 0 to 15 'palette 61 out (&h64),128+14 : out (&h63),i*4 70 out (&h61),i*2 : out (&h61),i*2 : out (&h61),i*1 + 13 80 next 100 p = 0 : a = 0 : gosub 10000 'charset in screen 5 format 110 for y = 0 to 15 'init two row of chars 115 for x = 0 to 31 : for i = 0 to 3 : out &h60,(x and 15)*17 : next i,x,y 200 p = 4 : a = 0 : gosub 10000 'second charset in screen 5 format 210 for y = 0 to 7 'init one row of chars 215 for x = 0 to 31 : for i = 0 to 3 : out &h60,((x+y) and 15)*17 : next i,x,y 299 '16bit nametable little endian 300 for y = 0 to 25 310 p = 7 : a = &hc000+64*2*y : gosub 10000 '64 chars wide, 2 byte per char 320 for x = 0 to 31 330 out &h60,x and 15 : out &h60,0 340 next x,y 399 'lower layer 16bit nametable little endian 400 for y = 0 to 25 410 p = 7 : a = &he000+64*2*y : gosub 10000 420 for x = 0 to 31 430 out &h60,0 and 15 : out &h60,0 440 next x,y 500 'sprite attribute table, 4 bytes per sprite: Y, pattern, X, todo(x high?) 510 p = 3 : a = &hfe00 : gosub 10000 515 for i = 0 to 15 520 sy = int(sin(i*2*3.1415926/16)*5+100) : ? sy 525 out &h60,sy : out &h60,2 : out &h60,i*16+3 : out &h60,0 530 next 9990 beep : sound 8,12 : for i = 1 to 2000 : next : beep 9999 stop 10000 'vram write address = p*65536 + a . out &h60 vpokes with autoincrement. 10005 out (&h64),0 'vram write mode: 0 10006 defusr1 = a 'to get at H,L 10010 xx = peek(&hf39c) : out (&h63),xx : '?xx; 10020 xx = peek(&hf39d) : out (&h63),xx : '?xx;"." 10030 out (&h63),p 'bit 7 address increment inhibit 10050 return 21000 'regs 21010 data 0,0,0,0 21020 data 0,0,&h05,0 21030 data &h82,0,0,0 21040 data 0,0,0,0 21050 data 0,0,0,0 21060 data 0,0,0,0 21070 data 0 50000 'Physical mapping: Addresses 00000-3FFFF in VRAM0 and 40000-7FFFF in VRAM1. 50010 '00000-3FDFF (Sprite) Pattern Data (Layer A) 50020 '3FE00-3FFFF Sprite Attribute Table 50030 '40000-7BFFF Pattern Data (Layer B) 50040 '7C000-7DFFF PNT(A) - Pattern Name Table (Layer A) 50050 '7E000-7FFFF PNT(B) - Pattern Name Table (Layer B)
