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■ 9.2 Priority and color calculation

The priority of the sprite and scroll screen is determined by the size of a 3-bit value called the priority number. A sprite can specify up to eight priority numbers, one of which can be selected for each character by the priority bit in the sprite data.
∙ When using the color calculation function between the sprite and the scroll screen, you can decide whether to perform color calculation according to the priority number value selected by the sprite character. In addition, a maximum of 8 color calculation ratios can be specified, and one of them can be selected for each character by the color calculation ratio bits in the sprite data.

■ Priority number selection

For the sprite priority number, one of the eight priority numbers is selected for each sprite character by the priority bit for the specified sprite type. If the priority bit for the specified sprite type is 2 bits or less, the missing bits are regarded as 0, and if there is no priority bit, all 3 bits are regarded as 0. If the sprite data is in RGB format, register 0 for sprite is selected.
Priority number register selection by priority bit value is shown in Table 9.2.

Table 9.2 Selection of sprite priority number register
Priority bit Selected priority number register
PR2PR1PR0
0 0 0 Sprite register 0 (1800F0H bit 2 ~ 0)
0 0 1 Sprite register 1 (1800F0H bit 10 ~ 8)
0 1 0 Sprite register 2 (1800F2H bit 2 ~ 0)
0 1 1 Sprite register 3 (1800F2H bit 10 ~ 8)
1 0 0 Sprite register 4 (1800F4H bit 2 ~ 0)
1 0 1 Sprite register 5 (1800F4H bit 10 ~ 8)
1 1 0 Sprite register 6 (1800F6H bit 2 ~ 0)
1 1 1 Sprite register 7 (1800F6H bit 10 ~ 8)

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