Chapter 13 Color Offset Function

The color offset function is a function that changes the screen color without changing the color RAM data by adding the offset value when outputting the color data of the sprite and each scroll screen, and is used for fade-in, fade-out, etc. increase.

■ 13.1 Color offset specification

For the color offset value, you can set two values, color offset A and color offset B, for each RGB, and you can specify which of these two values to use for each screen. The color offset value is 9-bit data corresponding to each of RGB, and in all cases where the color data as a result of adding to each of RGB becomes smaller than 00H, the color data is set to 00H and becomes larger than FFH. In all such cases, use FFH.

Since the processing of the color offset function is performed after the processing of the color calculation function, the color offset value is added to the color data of the result of the color calculation. Also, since the result screen of the color calculation is regarded as the screen of the top image, the color offset enable register is specified by the bit for the screen of the top image.

The color offset data is shown in Figure 13.1.

Figure 13.1 Color offset data

7 6 5 4 3 2 1 0
┌─┬─┬─┬─┬─┬─┬─┬─┐
│ Color data 8 bits │
└─┴─┴─┴─┴─┴─┴─┴─┘
　
＋　
　
8 7 6 5 4 3 2 1 0　
┌─┬─┬─┬─┬─┬─┬─┬─┬─┐
│ │ Color data 8 bits │
└─┴─┴─┴─┴─┴─┴─┴─┴─┘
Code　
↓　
　
7 6 5 4 3 2 1 0　
┌─┬─┬─┬─┬─┬─┬─┬─┐
│ Output color data 8 bits │
└─┴─┴─┴─┴─┴─┴─┴─┘

● Color offset enable register

The color offset enable register specifies whether to use the color offset function for each screen. A write-only 16-bit register located at address 180110H. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

CLOFEN 180110H

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

07 07	06 06	05 05	04	03 03	02 02	01 01	00
---	SPCOEN	BKCOEN	R0COEN	N3COEN	N2COEN	N1COEN	N0COEN

Color offset enable bit : Color offset enable bit

(N0COEN, N1COEN, N2COEN, N3COEN, R0COEN, BKCOEN, SPCOEN)
Specifies whether to use the color offset function.

N0COEN	180110H	Bit 0	For NBG0 (or for RBG1)
N1COEN	180110H	Bit 1	For NBG1 (or for EXBG)
N2COEN	180110H	Bit 2	For NBG2
N3COEN	180110H	Bit 3	For NBG3
R0COEN	180110H	Bit 4	For RBG0
BKCOEN	180110H	Bit 5	For BACK
SPCOEN	180110H	Bit 6	For sprites

xxCOEN	process
0	Do not use the color offset function
1	Use the color offset function

[Note] The bit name xx contains N0, N1, N2, N3, R0, BK, or SP.

When using the color calculation function, specify it with the color offset enable bit on the screen on the top image side.

● Color offset select register

The color offset select register specifies the color offset register to use for each screen. A write-only 16-bit register located at address 180112H. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

CLOFSL 180112H

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

07 07	06 06	05 05	04	03 03	02 02	01 01	00
---	SPCOSL	BKCOSL	R0COSL	N3COSL	N2COSL	N1COSL	N0COSL

Color offset select bit : Color offset select bit

(N0COSL, N1COSL, N2COSL, N3COSL, R0COSL, BKCOSL, SPCOSL)
Specifies the color offset register to use when using the color offset function.

N0COSL	180112H	Bit 0	For NBG0 (or for RBG1)
N1COSL	180112H	Bit 1	For NBG1 (or for EXBG)
N2COSL	180112H	Bit 2	For NBG2
N3COSL	180112H	Bit 3	For NBG3
R0COSL	180112H	Bit 4	For RBG0
BKCOSL	180112H	Bit 5	For BACK
SPCOSL	180112H	Bit 6	For sprites

xxCOSL	process
0	Use the value of color offset A
1	Use the value of color offset B

[Note] The bit name xx contains N0, N1, N2, N3, R0, BK, or SP.

When using the color calculation function, specify it with the color offset select bit on the screen on the top image side.

● Color offset register

The color offset register specifies each RGB value of the color offset value. This is a write-only 16-bit register located at addresses 180114H to 18011EH. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

COAR 180114H

15	14	13	12	11	Ten	09 09	08 08
---	---	---	---	---	---	---	COARD8

07 07	06 06	05 05	04	03 03	02 02	01 01	00
COARD7	COARD6	COARD5	COARD4	COARD3	COARD2	COARD1	COARD0

COAG 180116H

15	14	13	12	11	Ten	09 09	08 08
---	---	---	---	---	---	---	COAGR8

07 07	06 06	05 05	04	03 03	02 02	01 01	00
COAGR7	COAGR6	COAGR5	COAGR4	COAGR3	COAGR2	COAGR1	COAGR0

COAB 180118H

15	14	13	12	11	Ten	09 09	08 08
---	---	---	---	---	---	---	COABL8

07 07	06 06	05 05	04	03 03	02 02	01 01	00
COABL7	COABL6	COABL5	COABL4	COABL3	COABL2	COABL1	COABL0

COBR 18011AH

15	14	13	12	11	Ten	09 09	08 08
---	---	---	---	---	---	---	COBRD8

07 07	06 06	05 05	04	03 03	02 02	01 01	00
COBRD7	COBRD6	COBRD5	COBRD4	COBRD3	COBRD2	COBRD1	COBRD0

COBG 18011CH

15	14	13	12	11	Ten	09 09	08 08
---	---	---	---	---	---	---	COBGR8

07 07	06 06	05 05	04	03 03	02 02	01 01	00
COBGR7	COBGR6	COBGR5	COBGR4	COBGR3	COBGR2	COBGR1	COBGR0

COBB 18011EH

15	14	13	12	11	Ten	09 09	08 08
---	---	---	---	---	---	---	COBBL8

07 07	06 06	05 05	04	03 03	02 02	01 01	00
COBBL7	COBBL6	COBBL5	COBBL4	COBBL3	COBBL2	COBBL1	COBBL0

Color offset value bit: Color offset data bit

(COARD8 ~ COARD0, COAGR8 ~ COAGR0, COABL8 ~ COABL0, COBRD8 ~ COBRD0, COBGR8 ~ COBGR0, COBBL8 ~ COBBL0)
Set the RGB values of color offset A and color offset B respectively. Negative numbers should be set in 2's complement.

COARD8 ~ COARD0	180114H	Bits 8-0	For RED data with color offset A
COAGR8 ~ COAGR0	180116H	Bits 8-0	For GREEN data of color offset A
COABL8 ~ COABL0	180118H	Bits 8-0	For BLUE data with color offset A
COBRD8 ~ COBRD0	18011AH	Bits 8-0	For RED data with color offset B
COBGR8 ~ COBGR0	18011CH	Bits 8-0	For GREEN data of color offset B
COBBL8 ~ COBBL0	18011EH	Bits 8-0	For BLUE data with color offset B