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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 4 Scroll screen
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VDP2 User's Manual/Chapter 4 Scroll screen

■4.9 Bitmap

When displaying in bitmap format, choose from four sizes: 512 dots wide x 256 dots high, 512 dots wide x 512 dots high, 1024 dots wide x 256 dots high, or 1024 dots wide x 512 dots high. The bitmap pattern data of each dot that makes up the bitmap is stored in VRAM.

●Bitmap size

The types of bitmap sizes that can be selected differ between the normal scroll screen and the rotary scroll screen.
On a normal scroll screen, if you specify a high resolution graphic mode with a horizontal resolution of more than 512 pixels and select a bitmap size of 512 dots horizontally, the same picture will be repeated horizontally. Also, if you specify a dedicated monitor mode or double-dense interlace mode with a vertical resolution of more than 256 pixels and select a bitmap size of 256 dots vertically, the same picture will be repeated vertically.
Table 4.9 shows the bitmap sizes.

Table 4.9 Bitmap size
screen Selectable bitmap sizes
Normal scroll screen 512 dots horizontally x 256 dots vertically
512 dots horizontally x 512 dots vertically
1024 dots horizontally x 256 dots vertically
1024 dots horizontally x 512 dots vertically
rotating scroll screen 512 dots horizontally x 256 dots vertically
512 dots horizontally x 512 dots vertically

●Number of bitmap colors

The color formats for displaying bitmap format screens include a palette format in which the color RAM address is specified by combining the bitmap palette number and the dot color code in the bitmap pattern data, and a palette format in which the RGB data to be displayed is directly specified. It has RGB format. Table 4.10 shows the number of colors per bitmap and the number of bits per dot of bitmap pattern data for each color format. Also, set the bitmap color number in the character color number bit of the character control register.

Table 4.10 Number of bitmap colors
color format bitmap
Number of colors		 Number of bitmap pattern data bits per dot
palette 16 colors 4 bits
256 colors 8 bit
2048 colors 16 bits (only lower 11 bits are used)
RGB 32768 colors 16 bit
16.77 million colors 32 bits (only MSB and lower 24 bits are used)
[Note] When the color RAM mode is Mode 0 or Mode 2, 2048 colors become 1024 colors.

●Bitmap pattern

The VRAM capacity required per bitmap pattern varies depending on the bitmap size and number of bitmap colors (bitmap pattern data size). Additionally, the data structure of each bitmap pattern stored in VRAM changes as well. The bitmap size and number of bitmap colors can be set to exceed the VRAM capacity, but in that case the same picture will be repeated vertically. Table 4.11 shows the bitmap pattern capacity and Figure 4.17 shows the bitmap pattern configuration.
The boundary for storing bitmap patterns in VRAM is 20000H, regardless of the bitmap size or number of bitmap colors, and is specified using the map offset register.

Table 4.11 Bitmap pattern capacity per page
bitmap
size		 bitmap pattern
Data size		 bitmap color count Capacity per side detail
512 dots horizontally
Vertical 256 dots		 4 bits/dot 16 colors 64K bytes (512K bits) (1)→
8 bits/dot 256 colors 128K bytes (1M bit) (2)→
16 bits/dot 2048 colors, 32768 colors 256K bytes (2M bits) (3)→
32 bits/dot 16.77 million colors 512K bytes (4M bits) (4)→
512 dots horizontally
Vertical 512 dots		 4 bits/dot 16 colors 128K bytes (1M bit) (5)→
8 bits/dot 256 colors 256K bytes (2M bits) (6)→
16 bits/dot 2048 colors, 32768 colors 512K bytes (4M bits) (7)→
32 bits/dot 16.77 million colors 1024K bytes (8M bits) (8)→
1024 dots horizontally
Vertical 256 dots		 4 bits/dot 16 colors 128K bytes (1M bit) (9)→
8 bits/dot 256 colors 256K bytes (2M bits) (10)→
16 bits/dot 2048 colors, 32768 colors 512K bytes (4M bits) (11)→
32 bits/dot 16.77 million colors 1024K bytes (8M bits) (12)→
1024 dots horizontally
Vertical 512 dots		 4 bits/dot 16 colors 256K bytes (2M bits) (13)→
8 bits/dot 256 colors 512K bytes (4M bits) (14)→
16 bits/dot 2048 colors, 32768 colors 1024K bytes (8M bits) (15)→

Please click details in Table 4_11 for reference bitmap pattern configuration

●Bitmap palette number

The bitmap palette number is 3-bit data specified by the bitmap palette number register, and specifies the start address of the palette used for the bitmap pattern. Bitmap palette numbers are used only when the color format is palette format, not when the color format is RGB format. The palette number is added to the dot color code of the bitmap pattern to create an 11-bit dot color code, so the number of bits used changes depending on the number of colors per page. Figure 4.18 shows dot color data based on bitmap color numbers.

Figure 4.18 Dot color data by bitmap color number
●Number of bitmap colors: 16 colors
┌────────────────────┬───────────┐
│ Palette number     │ Dot color │
│                    │   code    │
├──┬──┬──┬──┬──┬──┬──┼──┬──┬──┬──┤
│ 6│ 5│ 4│ 3│ 2│ 1│ 0│ 3│ 2│ 1│ 0│
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
└────────┘└──────────┘ 
     ↑         ↑ 
     │     Fixed to 0 
     │ 
Specified by bitmap
palette number register 


●Number of bitmap colors: 256 colors
┌────────┬───────────────────────┐
│Palette │     Dot color code    │
│number  │                       │
├──┬──┬──┼──┬──┬──┬──┬──┬──┬──┬──┤
│ 6│ 5│ 4│ 7│ 6│ 5│ 4│ 3│ 2│ 1│ 0│
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
└────────┘ 
     ↑ 
Specified by bitmap
palette number register 


●Number of bitmap colors: 16 colors
┌────────────────────────────────┐
│         Dot color code         │
├──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┤
│10│ 9│ 8│ 7│ 6│ 5│ 4│ 3│ 2│ 1│ 0│
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘

●Special function bit

The special function bit is 2-bit data that specifies whether to use special functions for the bitmap pattern. The special function bits include a special priority bit that controls the priority number and a special color calculation bit that controls color calculation. For details on special priority bits, see " 11.2 Special Priority Function ." For details on color calculation bits, please refer to " 12.2 Special color calculation functions ".

●Bitmap palette number register

The bitmap palette number register specifies the palette number and special function bits when displaying the scroll screen in bitmap format. This is a 16-bit write-only register located at addresses 18002CH to 18002EH. The value is cleared to 0 after power-on or reset, so be sure to set it.

BMPNA 18002CH
   15   
   14   
   13   
   12   
   11   
   10   
   09   
   08   
 -
 -
 N1BMPR
 N1BMCC
 -
 N1BMP6
 N1BMP5
 N1BMP4

   07   
   06   
   05   
   04   
   03   
   02   
   01   
   00   
 -
 -
 N0BMPR
 N0BMCC
 -
 N0BMP6
 N0BMP5
 N0BMP4

BMPNB 18002EH
   15   
   14   
   13   
   12   
   11   
   10   
   09   
   08   
 -
 -
 -
 -
 -
 -
 -
 -

   07   
   06   
   05   
   04   
   03   
   02   
   01   
   00   
 -
 -
 R0BMPR
 R0BMCC
 -
 R0BMP6
 R0BMP5
 R0BMP4

　　　
Special priority bit (for bitmap) : Bit map special priority bit
(N0BMPR, N1BMPR, R0BMPR)
Specify the special priority bit when displaying the scroll screen in bitmap format.

N0BMPR 18002CH bit 5 For NBG0
N1BMPR 18002CH bit 13 For NBG1
R0BMPR 18002EH bit 5 For RBG0

For details on how to use this bit, see " 11.2 Special Priority Function ."

　　　
Bit map special color calculation bit
(N0BMCC, N1BMCC, R0BMCC)
Specify the special color calculation bit when displaying the scroll screen in bitmap format.

N0BMCC 18002CH bit 4 For NBG0
N1BMCC 18002CH bit 12 For NBG1
R0BMCC 18002EH bit 4 For RBG0

For details on how to use this bit, see ` `12.2 Special color calculation function ''.

　　　
Palette number bit (for bitmap) : Bit map palette number bit
(N0BMP6~N0BMP4, N1BMP6~N1BMP4, R0BMP6~R0BMP4)
Specify the upper 3 bits of the palette number when displaying the scroll screen in bitmap format.

N0BMP6～N0BMP4 18002CH bits 2-0 For NBG0
N1BMP6～N1BMP4 18002CH bits 10-8 For NBG1
R0BMP6～R0BMP4 18002EH bits 2-0 For RBG0

When the number of bitmap colors is 16, 0 is added to the lower 4 bits and used as a 7-bit palette number.

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★ HARDWARE Manual VDP2 User's Manual ★ Chapter 4 Scroll screen
Copyright SEGA ENTERPRISES, LTD., 1997