User:Lidnariq/Microchip-style PPU documentation

Microchip-style documentation format

REGISTER: PPUCTRL: PPU properties

W-0/0	W-0/0	W-0/0	W-0/0	W-0/0	W-0/0	W-0/0	W-0/0
NMIEN	EXTOUTEN	SPR8x16	BKGD	SPR	INC32	Y8	X8
bit 7							bit 0

Legend
R = Readable bit	W = Writable bit	U = Unimplemented bit, read as open bus
u = bit is unchanged	x = bit is unknown	-n/n = value on Power-on/all other resets
1 = bit is set	0 = bit is cleared	q = value depends on conditions

bit 7	NMIEN: NMI enable 1 = NMI is triggered at start of vblank, after 1 (or 51) post-render scanlines 0 = NMI is not triggered
bit 6	EXTOUTEN: External output Enable 1 = output bottom 4 bits of color on EXT pins 0 = accept bottom 4 bits of backdrop on EXT pins (background colors 1-3 are opaque; color 0 is transparent and from the external port)
bit 5	SPR8x16: Sprites size 1 = All sprites are 8x16 0 = All sprites are 8x8
bit 4	BKGD: Background tile location 1 = Background tiles are fetched from PPU $1xxx 0 = Background tiles are fetched from PPU $0xxx
bit 3	SPR: Sprite tile location 8x16 sprites: Don't care. 8x8 sprites: 1 = Sprite tiles are fetched from PPU $1xxx 0 = Sprite tiles are fetched from PPU $0xxx
bit 2	INC32: PPU address autoincrement step size 1 = PPU address increments by 32 after reads or writes to PPUDATA 0 = PPU address increments by 1 after reads or writes to PPUDATA
bit 1	Y8: 240s bit of Y scroll position 1 = Rendering will start in nametable at $2800 or $2C00 0 = Rendering will start in nametable at $2000 or $2400
bit 0	X8: 256s bit of X scroll position 1 = Rendering will start in nametable at $2400 or $2C00 0 = Rendering will start in nametable at $2000 or $2800

REGISTER: PPUMASK: PPU rendering modifications

W-0/0	W-0/0	W-0/0	W-0/0	W-0/0	W-0/0	W-0/0	W-0/0
BLUE	GREEN	RED	SPREN	BKGDEN	SPRCLIP	BKGDCLIP	MONO
bit 7							bit 0

Legend
W = Writable bit	0 = bit is cleared	-n/n = value on Power-on/all other resets

bit 7	BLUE: Blue emphasis 1 = (2C02, 2C07, Dendy) red and green dimmed, blues emphasized; (2C03,2C04,2C05) blue set to maximum brightness 0 = normal
bit 6	GREEN: Green emphasis 1 = (2C02) red and blue dimmed, green emphasized; (2C03,2C04,2C05) green set to maximum brightness; (2C07, Dendy) green and blue dimmed, red emphasized 0 = normal
bit 5	RED: Red emphasis 1 = (2C02) green and blue dimmed, red emphasized; (2C03,2C04,2C05) red set to maximum brightness; (2C07, Dendy) red and blue dimmed, green emphasized 0 = normal
bit 4	SPREN: Sprite rendering enable 1 = Sprites are drawn to screen, and PPU bus is active 0 = Sprites are not drawn
bit 3	BKGDEN: Background rendering enable 1 = Background is drawn to screen, and PPU bus is active 0 = Background is not drawn. If both SPREN and BKGDEN are clear, then the PPU bus is inactive
bit 2	SPRCLIP: Draw sprites in leftmost 8 pixels 1 = Sprites are visible in leftmost 8 columns 0 = Sprites are NOT visible in leftmost 8 columns. Sprite 0 doesn't trigger on pixels that are not drawn.
bit 1	BKGDCLIP: Draw backgrounds in leftmost 8 pixels 1 = Backgrounds are visible in leftmost 8 columns 0 = Backgrounds are NOT visible in leftmost 8 columns. Sprite 0 doesn't trigger on pixels that are not drawn.
bit 0	MONO: Monochrome display 1 = All PPU palette reads for any purpose (rendering or via PPUDATA) are masked with $30. 0 = PPU palette reads function as normal, specifying any value of the normal palette

REGISTER: PPUSTATUS: PPU status

R/HC-x/q	R/HC-0/u	R/HC-x/u	U-q	U-q	U-q	U-q	U-q
VBL	SPR0	SPROV	—	—	—	—	—
bit 7							bit 0

Legend
R = Readable bit	W = Writable bit	U = Unimplemented bit, read as open bus
u = bit is unchanged	x = bit is unknown	-n/n = value on Power-on/all other resets
0 = bit is cleared	q = value depends on conditions	HC = Cleared by hardware

bit 7	VBL: Vertical blanking 1 = An NMI would occur (or has occured) 0 = This register has already been read this frame or it's more than 20 scanlines after the start of vertical blanking.
bit 6	SPR0: Sprite 0 collision 1 = A pixel in sprite 0 has overlaid some opaque pixel from the background 0 = No pixel in sprite 0 has overlaid any opaque pixel in the background since 20 scanlines after the start of vertical blanking.
bit 5	SPROV: Sprite overflow 1 = More than 8 sprites attempted to be rendered on a scanline (but see Errata) 0 = No scanline has had more than 8 sprites on it this frame.
bit 4-0	Unimplemented: Read as PPU's open bus