Background

The Super Nintendo supports up to 4 background layers. The actual number of available background layers depends on the selected background mode, ranging from mode 0 through mode 7. The background mode also determines the number of available colors for each individual background layer. The background mode is set in the lower 3 bits of BGMODE.

Each background layer is made up of a set of tiles organized into one or more two-dimensional (32×32) tilemaps. All tiles for a background layer are either 8×8 (default) or 16×16 pixels. The tilesize for background layer 1, 2, 3 or 4 is set by bit 4, 5, 6 or 7 respectively of BGMODE.

An individual background layer can be set to one of 4 possible dimensions: 32×32, 64×32, 32×64 or 64×64 tiles. The dimensions for each background layer are set in the lower 2 bits of its corresponding screen configuration (BG1SC, BG2SC, BG3SC and BG4SC).

The overall size in pixels of a background layer is thus determined by its tile size and dimension settings, and varies between 256×256 and 1024×1024 pixels.

Bits 2-6 of a background layer's screen configuration refer to the VRAM segment where the background layer's (first) tilemap is stored. This 5-bit value is shifted left by 10 to obtain the address of the (first) tilemap in VRAM.

To pairs of 4 bits in BG12NBA or BG34NBA refer to the VRAM segment where each background layer's characters are stored. This 3-bit value (ignoring the most significant bit) is shifted left by 12 to obtain the address of the first character.

Each background layer can be enabled or disabled using corresponding bit (0-3) in TM.

See also: Tiles