Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual page 38

AGB Programming Manual
BG2CNT,BG3CNT [d13] Area Overflow Processing
When the display screen overflows the boundaries of the virtual screen
due to a rotation/scaling operation, this bit can be used to choose whether
the area of the screen into which the overflow occurs is displayed as
transparent or wraps around the display screen.
For information on scaling, see "6.1.7 BG Rotation and Scaling Features".
BG*CNT [d12-08] Screen Base Block Specification
Specifies the starting block in VRAM where screen data are stored.
(32 steps: 0-31; 2-Kbyte increments).
See section 6.1.3, VRAM Address Mapping of BG Data.
BG*CNT [d07] Color Mode
Specifies whether to reference BG character data in 16 color x 16 palette
format or 256 color x 1 palette format.
BG*CNT [d06] Mosaic
Turns mosaic processing for BG on and off.
BG*CNT [d03-02] Character Base Block Specification
Specifies the starting block in VRAM where the character data to be
displayed in the BG is stored.
(4 steps: 0-3; 16-Kbyte increments)
See section 6.1.3, VRAM Address Mapping of BG Data.
BG*CNT [d01-00] Priority Among BGs
With the default value (same priority value specified for all), the order of
priority is BG0, BG1, BG2, and BG3. However, this order can be changed
to any desired.
Values of 0 (highest priority) to 3 can be specified.
When the BG priority has been changed, care should be taken in
specifying the pixels used for color special effects.
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Rendering Functions
D.C.N. AGB-06-0001-002B4