★ 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, select from four sizes: width 512 dots x height 256 dots, width 512 dots x height 512 dots, width 1024 dots x height 256 dots, or width 1024 dots x height 512 dots. Stores the bitmap pattern data of each dot that makes up the bitmap 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 the 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 with a vertical resolution of more than 256 pixels or a double-dense interlaced mode, and you select a bitmap size with a vertical resolution of 256 dots, the same picture is repeated vertically.
The bitmap sizes are shown in Table 4.9.

Table 4.9 Bitmap size
screen Selectable bitmap size
Normal scroll screen 512 dots wide x 256 dots high
512 dots wide x 512 dots high
1024 dots wide x 256 dots high
1024 dots wide x 512 dots high
Rotating scroll screen 512 dots wide x 256 dots high
512 dots wide x 512 dots high

● Bitmap color count

For the color format for displaying the bitmap format screen, specify the palette format that specifies the color RAM address by combining the bitmap palette number and the dot color code in the bitmap pattern data, and directly specify the RGB data to be displayed. There is an RGB format. Table 4.10. Shows the number of colors per surface of the bitmap and the number of bits per dot of the bitmap pattern data in each color format. Also, set the number of bitmap colors to the number of character color bits in the character control register.

Table 4.10 Bitmap color count
Color format Bitmap color count Bitmap pattern data bits per dot
palette 16 colors 4 bits
256 colors 8 bits
2048 colors 16 bits (use only the lower 11 bits)
RGB 32768 colors 16 bit
16.77 million colors 32 bits (only MSB and lower 24 bits are used)
[Note] If the color RAM mode is mode 0 or mode 2, 2048 colors will be 1024 colors.

● Bitmap pattern

The amount of VRAM required per surface of a bitmap pattern varies depending on the bitmap size and the number of bitmap colors (bitmap pattern data size). In addition, the data structure of each bitmap pattern stored in VRAM changes as well. The bitmap size and the number of bitmap colors can be set to exceed the VRAM capacity, in which case the same picture will be repeated vertically. The bitmap pattern capacitance is shown in Table 4.11 and the bitmap pattern configuration is shown in Figure 4.17.
The boundary for storing the bitmap pattern in VRAM in VRAM is 20000H regardless of the bitmap size and the number of bitmap colors, and the specification is made in the map offset register.

Table 4.11 Bitmap pattern capacity per surface
Bitmap size Bitmap pattern data size Bitmap color count Capacity per side detail
Horizontal 512 dots x
Vertical 256 dots		 4 bits / dot 16 colors 64K bytes (512K bits) (1) →
8 bits / dot 256 colors 128K bytes (1M bits) (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) →
Horizontal 512 dots x
512 dots vertically		 4 bits / dot 16 colors 128K bytes (1M bits) (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 wide x
Vertical 256 dots		 4 bits / dot 16 colors 128K bytes (1M bits) (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 wide x
512 dots vertically		 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) →

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 RGB format. Since the palette number is added to the dot color code of the bitmap pattern to make an 11-bit dot color code, the number of bits used varies depending on the number of colors per surface. Figure 4.18 shows the dot color data based on the number of bitmap colors.

Figure 4.18 Dot color data based on the number of bitmap colors
● 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 number │ Dot color code │
├──┬──┬──┼──┬──┬──┬──┬──┬──┬──┬──┤
│ 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 the special function for the bitmap pattern. The special function bits include a special priority bit that controls the priority number and a special color operation bit that controls the color operation. For details on the special priority bit, see 11.2 Special Priority Function. For the color calculation bits, 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 for displaying the scroll screen in bitmap format. This is a write-only 16-bit register located at addresses 18002CH to 18002EH. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

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

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

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

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

　　　
Special priority bit (for bitmap) : Bit map special priority bit
(N0BMPR, N1BMPR, R0BMPR)
Specifies a special priority bit for 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, refer to "11.2 Special Priority Function".

　　　
Special color calculation bit (for bitmap) : Bit map special color calculation bit
(N0BMCC, N1BMCC, R0BMCC)
Specifies special color operation bits for 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, refer to "12.2 Special Color Arithmetic Function".

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

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

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

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