NFG Games + GameSX

Graphic VRAM

The structure of G-VRAM differs depending on the actual screen size and the number of colors. A total of 512 KB of VRAM is divided and allocated.

The pixel representation is a linear type and in any mode one pixel is represented by one word. In the 16/256 color display mode only the lower 4/8 bits are effective.

X = X coordinate in normal mode
Y = Y 〃
P = Plane number
ADR = 65536 color display mode address (X,Y)
BIT = 〃 bit position

Real screen 512×512 pixels、65536 color display

Valid bits	Full 16 bits
1 Row	1024 bytes(512 words)
Page 0	$c00000～$c7ffff

Real screen 512×512 pixels、256 color display:

Valid bits	Lower 8 bits
1 Row	1024 bytes(512 words)
Page 0	$c00000～$c7ffff
Page 1	$c80000～$cfffff

ADR = $c00000＋Y×1024＋X×2
BIT = P×8 ～ P×8＋7 for 8 bits

Real screen 512×512 pixels、16 colors

Valid bits	Lower 4 bits
1 Row	1024 bytes(512 words)
Page 0	$c00000～$c7ffff
Page 1	$c80000～$cfffff
Page 2	$d00000～$d7ffff
Page 3	$d80000～$dfffff

ADR = $c00000＋Y×1024＋X×2
BIT = P×4 ～ P×4＋3 for 4 bits

Real screen 1024×1024 pixels、16 colors:

Valid bits	Lower 4 bits
1 Row	2048 bytes(1024 words)
Page 0	$c00000～$dfffff

ADR = $c00000＋(Y＆511)×1024＋(X＆511)×2
BIT = (Y≧512)×8＋(X≧512)×4 ～
      (Y≧512)×8＋(X≧512)×4＋3 for 4 bits

Text VRAM

T-VRAM has a real screen size of 1024×1024 pixels fixed to 16 color display and 4 planes for a total of 512KB. Pixel representation is planar type, 1 word is 16 horizontal pixels. Each plane represents 1 bit of the 4-bit palette code.

1 Row	128 bytes(64 words)
Page 0	$e00000～$e1ffff
Page 1	$e20000～$e3ffff
Page 2	$e40000～$e5ffff
Page 3	$e60000～$e7ffff