Chapter 2: Display Functions; General Display Functions; Character Composition - Nintendo GAME BOY Programming Manual

Game Boy Programming Manual

CHAPTER 2: DISPLAY FUNCTIONS

1. GENERAL DISPLAY FUNCTIONS

1.1 Character Composition

!
The basic character size is an 8 x 8-dot composition.
!
With characters of the basic size:
•
128 OBJ-only characters are available (256 with CGB)
•
128 BG-only characters are available (256 with CGB)
•
128 characters can be registered both as OBJ and BG characters (256 with
CGB)
!
On DMG, characters can be represented using 4 shades of gray (including
transparent). On CGB, characters can be represented using 32 shades for each
color of RGB.
!
The basic character size can be switched to an 8 x 16-dot composition for OBJ
characters only. In this case, however, only even-numbered character codes can
be specified. Even if an odd-numbered character code is specified, the display will
be the same as that seen with an even-numbered code.
!
Up to 40 OBJ characters can be displayed in a single screen, and up to 10
characters can be displayed on each horizontal line.
!
The display data for OBJ characters are as follows:
•
y-axis coordinate
•
x-axis coordinate
•
Character code
•
Attribute data
!
Data are written to OAM from working RAM by DMA transfer.
!
OBJ characters are automatically displayed to the screen using the data written to
OAM.
!
Data specification ranges for OBJ characters:
• 00 ≤ character code ≤ FFh
• 00 ≤ X ≤ FFh
• 00 ≤ Y ≤ FFh
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