<43/86>VDP2 User's Manual/6.3 Rotation Parameter Control-3

★ 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 table address register

The rotation parameter table address register specifies the start address of the rotation parameter table. This is a 16-bit write-only register located at addresses 1800BCH to 1800BEH. The value is cleared to 0 after power-on or reset, so be sure to set it.

RPTAU 1800BCH

-	-	-	-	-	-	-	-
15	14	13	12	11	10	09	08

07
06
05
04
03
02
01
00

-
-
-
-
-
RPTA18
RPTA17
RPTA16

07	06	05	04	03	02	01	00
-	-	-	-	-	RPTA18	RPTA17	RPTA16

RPTAL 1800BEH

RPTA15	RPTA14	RPTA13	RPTA12	RPTA11	RPTA10	RPTA9	RPTA8
15	14	13	12	11	10	09	08

07
06
05
04
03
02
01
00

RPTA7
RPTA6
RPTA5
RPTA4
RPTA3
RPTA2
RPTA1
-

Rotation parameters table address bit (RPTA18~RPTA1)

07	06	05	04	03	02	01	00
RPTA7	RPTA6	RPTA5	RPTA4	RPTA3	RPTA2	RPTA1	-

Specify the start address of the rotation parameter table.

RPTA18~RPTA16	1800BCH	bits 2-0
RPTA15～RPTA1	1800BEH	bits 15 to 1

The RPTA6 bit is ignored even if data is written to it. It is fixed to 0 for rotation parameter A and 1 for rotation parameter B.

The actual start address of the rotation parameter table is calculated using the following formula. If the VRAM capacity is 4Mbits, the most significant bit of the address is ignored.


(Start address of rotation parameter A)
   =(Rotation parameter table address register value upper 12 bits) x 100H
   +(Lower 5 bits of rotation parameter table address register value) x 4H

(Start address of rotation parameter B)
   =(Rotation parameter table address register value upper 12 bits) x 100H
   +(Rotation parameter table address register value lower 5 bits) x 4H+80H

For example, if you specify 00170H or 00130H, the start address of rotation parameter A will be 00260H, and the start address of rotation parameter B will be 002E0H.

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