nngs1024.txt

Memory Map for 1024x32 Number Nine Graphics cards

A000-AFFFF	64K Display buffer
C0000		GDC Write Parameter, Read Status
C0001		GDC Write Command, Read Data

C0400		Bank select  (4 bits)

C0700	3400	FF	ZOOM 1	(FF default, 00 more blowup)
C0701	3401	FF	ZOOM 2	(FF default, 00 more blowup)
C0702	3402	FF	ZOOM 4	(FF default, 00 more blowup)
C0703	3403	FF	ZOOM 8	(FF default, 00 more blowup)
C0704	3404	FF	MODE 1	lsb (00 or FF) see below
C0705	3405	00	MODE 2	msb (00 or FF) see below
C0706	3406	00	OVERLAY Select (00 ls nibble, FF ms nibble)
C0707	3407	FF	BUS ENABLE (00 disable, FF enable)
	
C1000-C1FFF	16x256 x 8 bit Red Look up table
C2000-C2FFF	16x256 x 8 bit Green Look up table
C3000-C3FFF	16x256 x 8 bit Blue Look up table


MODE BANK ADDR	Data
---- ---- ----	----
Gun mode		successive bytes pixels
  00 00XX XXXX	Red bytes
  00 01XX XXXX	Green bytes
  00 10XX XXXX	Blue bytes
  00 11XX XXXX	Overlay bytes
  
Concurrent mode: 8 bit emulation (overlay active) (clear faster)
  01 00XX XXXX	Read Red; Write all Red, Green and Blue bytes
  01 01XX XXXX	Read Green; Write all Red, Green and Blue bytes
  01 10XX XXXX	Read Blue; Write all Red, Green and Blue bytes
  01 11XX XXXX	Overlay bytes
  
Pixel mode
  10 00XX XXXX	Top 1/4 screen R byte, G byte, B byte, O byte, R ...
  10 01XX XXXX	2nd 1/4 screen
  10 10XX XXXX	3rd 1/4 screen
  10 11XX XXXX	bottom 1/4 screen
  
Pixel mode Write Protect overlay
  11 00XX XXXX	Top 1/4 screen R, G, B, O (write protected), R ...
  11 01XX XXXX	2nd 1/4 screen
  11 10XX XXXX	3rd 1/4 screen
  11 11XX XXXX	bottom 1/4 screen
    
Color Look Up table (LUT)

Three Look Up tables: 4K x 8 each gun.
12 bit address in and 8 bit data out.

4 bits are the same for each color gun (high or low nib of overlay byte)
8 bits for each color gun come from the R, G and B bytes of the pixel