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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

■4.10 Display area

The display area of the scroll screen changes depending on the register settings. If the display coordinate value exceeds the display area on the normal scroll screen, the image in the display area will be displayed repeatedly. If the displayed coordinate value exceeds the display area on a rotating scroll screen, it will be processed according to the register settings.

●Display area

The display area changes depending on the plane size if the scroll screen display format is cell format, and changes depending on the bitmap size if the scroll screen display format is bitmap format. Also, for NBG0 and NBG1, it changes depending on the setting of reduced display up to 1/4. The display areas are shown in Tables 4.12 and 4.13.

Table 4.12 Display area of normal scroll screen
Display format Reduce settings plane size bitmap size Display area
cell format No reduction
or
Possible up to 1/2		 1 horizontal page x
1 page vertically		 − 0≦X＜ 1024,0≦Y＜ 1024
2 horizontal pages ×
1 page vertically		 − 0≦X＜ 2048,0≦Y＜ 1024
2 horizontal pages ×
2 pages vertically		 − 0≦X＜ 2048,0≦Y＜ 2048
Possible up to 1/4 1 horizontal page x
1 page vertically		 − 0≦X＜ 1024,0≦Y＜ 2048
2 horizontal pages ×
1 page vertically		 − 0≦X＜ 2048,0≦Y＜ 2048
bitmap
format		 − − 512 dots horizontally
Vertical 256 dots		 0≦X＜ 512,0≦Y＜ 256
− 512 dots horizontally
Vertical 512 dots		 0≦X＜ 512,0≦Y＜ 512
− 1024 dots horizontally
Vertical 256 dots		 0≦X＜ 1024,0≦Y＜ 256
− 1024 dots horizontally
Vertical 512 dots		 0≦X＜ 1024,0≦Y＜ 512

Table 4.13 Display area of rotating scroll screen
Display format plain size bitmap size Display area
cell format 1 horizontal page x
1 page vertically		 − 0≦X＜ 2048,0≦Y＜ 2048
2 horizontal pages ×
1 page vertically		 − 0≦X＜ 4096,0≦Y＜ 2048
2 horizontal pages ×
2 pages vertically		 − 0≦X＜ 4096,0≦Y＜ 4096
bitmap format − 512 dots horizontally
Vertical 256 dots		 0≦X＜ 512,0≦Y＜ 256
− 512 dots horizontally
Vertical 512 dots		 0≦X＜ 512,0≦Y＜ 512

●Screen overflow processing

When displaying a rotary scroll screen, select one of the following four options and set it in the register when the display coordinate value of the calculation result exceeds the specified display area. Settings for screen overflow processing are not performed for RBG0 and RBG1, but for the scroll screen using rotation parameter A and the scroll screen using rotation parameter B.

  1. Outside the display area, the image set in the display area is repeated.

  2. Outside the display area, repeats the character pattern specified in the screen over pattern name register (only when the rotating scroll screen is in cell format).

  3. Make everything outside the display area transparent.

  4. Force display area to 0≦X regardless of plane size or bitmap size＜ 512, 0≦Y＜ 512 to make everything outside that area transparent.

●Screen over pattern name

When setting the screen overflow processing to repeat the specified character pattern, specify the pattern name data in the 16-bit screen overflow pattern name register. The screen-over pattern name data specified in the register is treated in the same way as if the data size of the pattern name table on the scroll surface is 1 word, and the missing bits are filled using the auxiliary data of the lower 10 bits of the pattern name control register. is supplemented to create a total of 26 bits of screen over pattern name data. The bit configuration of the screen over pattern name register is the same as when the pattern name data size is 1 word, as shown in " Pattern Name Data " in " 4.6 Pattern Name Table ", and the character size, number of character colors, and character It changes depending on the number assistance mode. Also, the size of the repeated character pattern follows the character size setting.
The 16-bit screen over pattern name data is specified for the scroll screen by rotation parameter A and the scroll screen by rotation parameter B, but the 10-bit auxiliary data specified by the pattern name control register is specified for RBG0 and RBG1. Please note that the Also, screen over pattern name data cannot be used when displaying a rotating scroll screen in bitmap format.

●Screen over pattern name register

The screen over pattern name register specifies the pattern name data when the character pattern is set to repeat during screen over processing on a rotating scroll screen. This is a 16-bit write-only register located at addresses 1800B8H to 1800BAH. The value is cleared to 0 after power-on or reset, so be sure to set it.

OVPNRA 1800B8H
   15   
   14   
   13   
   12   
   11   
   10   
   09   
   08   
 RAOPN15
 RAOPN14
 RAOPN13
 RAOPN12
 RAOPN11
 RAOPN10
 RAOPN9
 RAOPN8

   07   
   06   
   05   
   04   
   03   
   02   
   01   
   00   
 RAOPN7
 RAOPN6
 RAOPN5
 RAOPN4
 RAOPN3
 RAOPN2
 RAOPN1
 RAOPN0

OVPNRB 1800BAH
   15   
   14   
   13   
   12   
   11   
   10   
   09   
   08   
 RBOPN15
 RBOPN14
 RBOPN13
 RBOPN12
 RBOPN11
 RBOPN10
 RBOPN9
 RBOPN8

   07   
   06   
   05   
   04   
   03   
   02   
   01   
   00   
 RBOPN7
 RBOPN6
 RBOPN5
 RBOPN4
 RBOPN3
 RBOPN2
 RBOPN1
 RBOPN0

　　

Over pattern name bit : Over pattern name bit (RAOPN15～RAOPN0, RBOPN15～RBOPN0)
Specify the pattern name data when setting screen over processing that repeats character patterns.

RAOPN15～RAOPN0 1800B8H bits 15-0 For rotation parameter A
RBOPN15~RBOPN0 1800BAH bits 15-0 For rotation parameter B

The bit configuration is the same as when the pattern name table data size is 1 word, and changes depending on the character size, number of character colors, and character number assistance mode settings.
This register is used for the scroll screen using rotation parameter A and the scroll screen using rotation parameter B, but the character size and character number auxiliary mode that determine the bit configuration are used for RBG0 and RBG1. Therefore, be careful when displaying screens with rotation parameter A and rotation parameter B on RBG0 at the same time.

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