Fix layer

The fix layer is a non-scrollable, tile based layer with transparency which has the highest priority on the display (it always overlaps sprites). It is almost always used to display text or HUDs.

Graphics format

Tiles used are 8x8 pixels, stored in the S ROMs, or in FIX files before getting loaded to PSRAM in CD systems. In MVS systems, the onboard fix tileset is stoed in the SFIX ROM.

The tiles graphics are in 4BPP (15 colors + transparency) and can be individually mapped to the first 16 palettes.

See Fix graphics format for more details.

Fix map

File:Fixlayout.png

Fix layout. The grey area is part of the display but only the area in the red rectangle should be used.

The map is 40x32 tiles but only 40x28 tiles are drawn to the screen. Therefor, there are 2 hidden lines of tiles at the beginning and the end of the map. Some games also don't use the leftmost and rightmost columns, as some misaligned CRT screens (?) can cut them off.

Tiles are mapped from up to bottom, and left to right (see layout). The VRAM_MOD ($3C0004) register can be set to 32 instead of 1 if tile have to be updated in lines. See Displaying text.

The base address in VRAM for the map is $7000. Each tile uses one 16bit word:

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	Palette number				Tile number