<20/86>VDP2 User's Manual/4.2 Scroll screen configuration

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

▲ Back ｜ Forward ▼

VDP2 User's Manual/Chapter 4 Scroll screen

■4.2 Scroll screen configuration

There are two screen formats for the scroll screen: cell format and bitmap format.

●Cell format

The cell-format scrolling screen has a "cell" which is a picture pattern of 8 dots horizontally x 8 dots vertically, a "character pattern" which arranges cells 1 horizontally x 1 vertically, or 2 horizontally x 2 vertically, and a character pattern horizontally. "Page" is arranged in 32 x 32 vertically or 64 x 64 vertically; "Plain" is arranged in 1 horizontal x 1 vertical, 2 horizontal x 1 vertical, or 2 horizontal x 2 vertical; plain is 2 horizontal x vertical. It consists of "maps" arranged in 2 (for normal scroll screen) or 4 horizontally x 4 vertically (for rotating scroll screen). Figure 4.1 shows the structure of the scroll screen in cell format.

Figure 4.1 Structure of cell format scroll screen

Cell data is the dot color data stored in VRAM as a character pattern table. Color data can be 4, 8, 16, or 32 bits depending on the number of character colors. Character pattern data consists of 1 or 4 cell data arranged in a row. Page data stores character pattern name data (address of character pattern data) as a pattern name table. A plain is a set of 1, 2, or 4 page data. Map specifies the start address of the pattern name table in the map register and map offset register. Figure 4.2 shows the correspondence between the cell format scroll screen configuration and data settings.

Figure 4.2 Correspondence between cell format scroll screen configuration and data settings

[note]
The size of the character pattern and plane changes depending on the register settings, and the size of the map changes depending on the type of scroll screen. Figure 4.2 is an example of a character pattern of 2 cells horizontally x 2 cells vertically, a plane of 2 pages horizontally x 2 pages vertically, and a normal scroll screen (2 planes horizontally x 2 planes vertically).

●Bitmap format

A scroll screen in bitmap format consists of a bitmap pattern with a size of 512 dots or 1024 dots horizontally and 256 dots or 512 dots vertically. When displaying the screen in bitmap format, set the bitmap size in a register and store the bitmap pattern of the set size in VRAM.
Figure 4.3 shows the configuration of the bitmap format scroll screen, and Figure 4.4 shows the relationship between the bitmap format scroll screen and registers.

Figure 4.3 Configuration of bitmap format 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

Figure 4.4 Relationship between bitmap format scroll screen configuration and data settings

Map offset
 register                 Character control
┌──────────┐                  register
│Map offset│→┌────────────┐ ┌──────────┐ 
└──────────┘ │   Dot 0    │←│Number of │ 
             │ color data │ │character │ 
             │            │ │  colors  │ 
             ├────────────┤ └──────────┘ 
             │            │
             │            │
             │            │
   Bitmap    │            │
   format    │            │
  ┌───┬───┐  │            │
  │   │   │  │            │
  │   │   │  │   Bitmap   │ 
┌→├───┼───┤  │            │
│ │   │   │  │            │
│ │   │   │  │            │
│ └───┴───┘  │            │
│            │            │
│            │            │
│            │            │
│            └────────────┘
│
│Character control
│   register
│ ┌───────────┐
└─┤Bitmap size│
  └───────────┘

▲ Back ｜ Forward ▼

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