Nintendo DMG-01 - Game Boy Console Manual page 130

4.5. Commands
The tile map consists of a tile number byte & a tile
attribute byte at each position on the map. A total of
32 lines are downloaded even though the last 4 lines
are not visible. This would equal 64 bytes per line and
a total of 2048 bytes per map. Next, a 64 x 2 byte
color palette for the map is downloaded. The first
palette entry color is transparent. Use this color to
display regular GB screen underneath.
The tile number comes before the tile attribute of
each position. There can be up to 1024 tiles from which
to select. The SGB only supports 256 so bits 0 & 1 of
the tile attribute must be set to 0. Here are the tile
attributes I understand so far:
Bit 7 - Vertical flip tile
Bit 6 - Horizontal flip tile
Bit 5 - Does nothing (Set to 0.)
Bit 4 - Select Major Palette MSB (Usually set to 1.)
Bit 3 - Select Major Palette
Bit 2 - Select Major Palette LSB
Bit 1 - Tile # MSB (Most significant bit) (Set to 0.)
Bit 0 - Tile # NSB (Next most significant bit) (Set to
0.)
This is often called the SGB border but in fact it
covers the whole SNES screen. The Major Palette select
has 8 different settings. Only the last 4 - 7 are
normally used thought to access all 64 colors
transfered with cmd (#14).
(NOTE: If using 'gif2sopt.exe' to generate a border,
the range of the palette selections is 1-8 so select
palette 5 since that program only allows up to 16
colors.)
Page 130
Game Boy
-
TM
CPU Manual
V 1.01