Ports and VDP registers which are important for the video facilities as used in the NMS8280.

Ports

Port F6h

bit 7		self test (1 = aan)
bit 6		digitize enable (0 = aan)
bit 5		mix (0 = 1/2 impose)
bit 4		black / white (0 = aan)
bits 3-0	unused

Thansk to Albert Beevendorp and Koen van Hartingsveldt.

Note that the Basic SET VIDEO command does not control port F6 in anyway. 
Bit 5 and 6 has to be altered in combination with the SET VIDEO command.

F7 A/V control

b0    audio R  write Low mixing off
b1    audio L  write Low mixing off
b2    select video input low RGB SCART connector	
b3    detect video input read low no video present
b4    AV control write low:  TV
b5    YM control write low TV
b6    inverse of bit 4 of VDP register 9 (CBD), write
b7    inverse of bit 5 of VDP register 9 (TP), write  

Note that the SET VIDEO command in Basic controls the I/O port F7.


   VDP() reg.  7    6     5     4     3     2     1     0
   -------------------------------------------------------
     0    0    O   DG    IEO   IE1   M5    M4    M3     D
     1    1    O   BLK   IE2   M1    M2     O    SZ    MAG
     9    8   MSE  LCS   TP    CBD  VRS1  VRS0   SBD   B/W
    10    9   LN    O    SYM1  SYM0  IL    E/O   NTSC  DCD

 DG   -Digitize
 IE0  -Vertical Retrace Interrupt Enable 
 IE1  -Horizontal Retrace inerrupt Enable      
 IE2  -Light pen/mouse Interrupt Enable

 M5/1 -M5 M4 M3 M2 M1
       0  0  0  0  0  SCREEN-1
       0  0  0  0  1  SCREEN-0 (40 chars)
       0  0  0  1  0  SCREEN-3
       0  0  1  0  0  SCREEN-2
       0  1  0  0  0  SCREEN-4
       0  1  0  0  1  SCREEN-0 (80 tekens)
       0  1  1  0  0  SCREEN-5
       1  0  0  0  0  SCREEN-6
       1  0  1  0  0  SCREEN-7
       1  1  1  0  0  SCREEN-8

 D    -External VDP-input
 BLK  -Enable/Disable Display
 SZ   -Sprite size
 MAG  -Magnify Sprites
 MSE  -Light pen/mouse (1=muis)
 LC5  -Light pen/coincidence select (1=light pen)
 TP   -Transparant mode (1= color 0 niet transparant)
 CBD  -Color bus Direction

VRS1/0-Video RAM select
       VRS1  VRS0
         0     0  -1*16 Kb
         0     1  -4*16 Kb
         1     0  -1*64 Kb
         1     1  -64 Kb High Speed

 SPD  -Sprite disable
SYM0/1-Synchronisatie Mode
       SYM1  SYM0
         0     0  -Intern
         0     1  -Mix
         1     0  -Extern (Digitize)
         1     1  -none

 IL   -Interlaced Mode
 E/O  -Even/odd Display
 NTSC -TV/Monitor Select
 DCD  -Dot Clock Direction