<40/86> VDP2 User's Manual / 6.2 Rotation Scroll Screen Display Control

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

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VDP2 User's Manual / Chapter 6 Rotating Scroll Screen

■ 6.2 Rotation scroll screen display control

The rotation scroll screen has two sides, RBG0 and RBG1, and if only one side is displayed, RBG0 is displayed. When displaying RBG1, you must also display RBG0, in which case the normal scroll screen cannot be displayed at all.
When displaying the rotary scroll screen, the image data (pattern name table and character pattern table, or bitmap pattern) cannot be used in common with the image data for the normal scroll screen. It is also not possible to share the image data of RBG0 and RBG1. In addition, the image data of the rotary scroll screen must be stored in different VRAMs. Of the image data, the pattern name table of RBG1 is to be stored in VRAM-B1 and the character pattern table is to be stored in VRAM-B0.

When RBG0 needs coefficient data only for each line, the coefficient table can be stored in any bank of VRAM, but when it is required for each dot, it must be stored in a bank separate from the image data. It will not be.
The registers that control the display of the rotary scroll screen include the screen display enable register and the RAM control register. The screen display enable register controls the screen display and the transparent code. The contents of the register are the same as the normal scroll screen. For details, refer to "4.1 Screen Display Control".

● RAM control register

The RAM control register specifies the banking of VRAM, the intended use of VRAM on the rotating scroll screen, and the color RAM mode. A read-write 16-bit register located at address 18000EH. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

RAMCTL 18000EH

CRKTE	---	CRMD1	CRMD0	---	---	VRBMD	VRAMD
15	14	13	12	11	Ten	09 09	08 08

07 07
06 06
05 05
04
03 03
02 02
01 01
00
RDBSB11
RDBSB10
RDBSB01
RDBSB00
RDBSA11
RDBSA10
RDBSA01
RDBSA00

Color RAM coefficient table enable bit: Color RAM coefficient table enable bit ( CRKTE), bit 15

07 07	06 06	05 05	04	03 03	02 02	01 01	00
RDBSB11	RDBSB10	RDBSB01	RDBSB00	RDBSA11	RDBSA10	RDBSA01	RDBSA00

See 6.4 Coefficient Table Control.

Color RAM mode bits : Color RAM mode bits (CRMD1, CRMD0), bits 13, 12

Refer to " 3.4 Color RAM Mode".
When the CRKTE bit is set to 1, set the color RAM mode to mode 1. At that time, the latter half of the color RAM (100800H to 100FFFH) is used for the coefficient table data, so the color data cannot be stored.

VRAM mode bits : VRAM mode bits (VRAMD, VRBMD), bits 9, 8

See 3.2 VRAM Bank Split.

Rotation data bank select bit: Data bank select bit

(RDBSA01, RDBSA00, RDBSA11, RDBSA10, RDBSB01, RDBSB00, RDBSB11, RDBSB10)
Specifies the purpose of using VRAM on the rotary scroll screen. This bit is valid only when displaying a rotating scroll screen.

RDBSA00, RDBSA01	18000EH	Bits 1,0	For VRAM-A0 (or for VRAM-A)
RDBSA10, RDBSA11	18000EH	Bits 3,2	For VRAM-A1
RDBSB00, RDBSB01	18000EH	Bits 5,4	For VRAM-B0 (or for VRAM-B)
RDBSB10, RDBSB11	18000EH	Bits 7,6	For VRAM-B1

RDBSx1	RDBSx0	Purpose of use of VRAM
0	0	Not used as RAM for RBG0
0	1	RBG0 coefficient table RAM
1	0	RAM for pattern name table of RBG0
1	1	For RBG0 character pattern table (or bitmap pattern) RAM

Note The x in the bit name can be A0, A1, B0, or B1.

If VRAM is not divided into banks, the bits for VRAM-A0 will be used for VRAM-A and the bits for VRAM-B0 will be used for VRAM-B.
If you do not need coefficient data for each dot, you do not need to set the coefficient table RAM (01B).
When displaying in bitmap format, it is not necessary to set RAM (10B) for the pattern name table.
The setting of the VRAM cycle pattern register of the VRAM bank specified for the RAM for rotary scrolling is ignored.
If the image data read address is not in the specified bank, the data will not be read and the correct screen display will not be possible.
When displaying RBG1, be sure to set 00B for the VRAM-B0 and VRAM-B1 bits.
The read address of the coefficient data was not the address in the specified bank

In that case, the coefficient data will not be read and the correct screen display will not be possible.
When storing the coefficient table in color RAM, do not set the coefficient table RAM (01B) of RBG0.
When the CRKTE bit is set to 1, do not specify that 4 banks of VRAM should be used as RAM for coefficient table data.

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