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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 6 Rotating scroll screen
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VDP2 User's Manual/Chapter 6 Rotating scroll screen

●Rotation parameter mode register

The rotation parameter mode register controls the rotation parameter table used for RBG0. This is a 16-bit write-only register located at address 1800B0H. The value is cleared to 0 after power-on or reset, so be sure to set it.

RPMD 1800B0H
   15   
   14   
   13   
   12   
   11   
   10   
   09   
   08   
 -
 -
 -
 -
 -
 -
 -
 -

   07   
   06   
   05   
   04   
   03   
   02   
   01   
   00   
 -
 -
 -
 -
 -
 -
 RPMD1
 RPMD0

Rotation parameters mode bit : Rotation parameters mode bit (RPMD1, RPMD0), bits 1, 0
Specify which rotation parameter, A or B, to use when displaying RBG0.

RPMD1 RPMD0 mode Rotation parameters to use and how to use them
0 0 0 Rotation parameter A
0 1 1 Rotation parameter B
1 0 2 Coefficient data read from the coefficient table of rotation parameter A
Switch between image A and image B depending on the data
1 1 3 Image A and image B by rotation parameter window
switch

The value of this bit is always valid, so be careful when rewriting it.
When mode 2 is specified, when reading coefficient data dot by dot from the coefficient table for rotation parameter A, it is not possible to read coefficient data dot by dot from the coefficient table for rotation parameter B. Therefore, even if you specify a register to read coefficient data dot by dot from the coefficient table for rotation parameter B, it will be ignored.

In mode 3, coefficient data can be read dot by dot from both the coefficient table for rotation parameter A and the coefficient table for rotation parameter B.
When displaying RBG1, be sure to set it to mode 0.

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★ HARDWARE Manual VDP2 User's Manual ★ Chapter 6 Rotating scroll screen
Copyright SEGA ENTERPRISES, LTD., 1997