★ 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. A write-only 16-bit register located at address 1800B0H. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

RPMD 1800B0H
 15
 14
 13
 12
 11
 Ten
 09 09
 08 08
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 07 07
 06 06
 05 05
 04
 03 03
 02 02
 01 01
 00
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 RPMD1
 RPMD0

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

RPMD1 RPMD0 mode Rotation parameters to use and how to use
0 0 0 Rotation parameter A
0 1 1 Rotation parameter B
1 0 2 The image of A and the image of B are switched according to the coefficient data read from the coefficient table of the rotation parameter A.
1 1 3 Switch between image A and image B by rotation parameter window

The value of this bit is always valid, so be careful when you rewrite it.
When mode 2 is specified, when reading the coefficient data for each dot from the coefficient table for rotation parameter A, the coefficient data for each dot cannot be read from the coefficient table for rotation parameter B. Therefore, even if the register is specified to read the coefficient data dot by dot from the coefficient table for rotation parameter B, it is 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.
If you want to display RBG1, be sure to set it to mode 0.

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