User:Lidnariq/Microchip-style PPU documentation: Difference between revisions

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(Ham together something that looks like microchip formatting)
(→‎Microchip-style documentation format: may as well finish the bitfields, even if it's never useful anywhere else)
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== Microchip-style documentation format ==
== Microchip-style documentation format ==
'''REGISTER: PPUCTRL: PPU properties'''
===REGISTER: PPUCTRL: PPU properties===


{| class="tabular"
{| class="tabular"
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1 = Rendering will start in nametable at $2400 or $2C00<br/>
1 = Rendering will start in nametable at $2400 or $2C00<br/>
0 = Rendering will start in nametable at $2000 or $2800
0 = Rendering will start in nametable at $2000 or $2800
|}
===REGISTER: PPUMASK: PPU rendering modifications===
{| class="tabular"
|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 || SPR || BKGD || SPRCLIP || BKGDCLIP || MONO
|-
| bit 7 || colspan=6| || bit 0
|}
{| style="border:1px solid black;"
| '''Legend'''
|-
| W = Writable bit &nbsp; || 0 = bit is cleared &nbsp; || -n/n = value on Power-on/all other resets
|}
{|
| style="width:4em;"|bit 7 || '''BLUE''': Blue emphasis<br/>
1 = (2C02, 2C07, Dendy) red and green dimmed, blues emphasized; (2C03,2C04,2C05) blue set to maximum brightness <br/>
0 = normal
|-
| bit 6 || '''GREEN''': Green emphasis<br/>
1 = (2C02) red and blue dimmed, green emphasized; (2C03,2C04,2C05) green set to maximum brightness; (2C07, Dendy) '''green''' and blue dimmed, '''red''' emphasized<br/>
0 = normal
|-
| bit 5 || '''RED''': Red emphasis<br/>
1 = (2C02) green and blue dimmed, red emphasized; (2C03,2C04,2C05) red set to maximum brightness; (2C07, Dendy) '''red''' and blue dimmed, '''green''' emphasized<br/>
0 = normal
|-
| bit 4 || '''SPR''': Sprite rendering enable<br/>
1 = Sprites are drawn to screen, and PPU bus is active<br/>
0 = Sprites are not drawn
|-
| bit 3 || '''BKGD''': Background rendering enable<br/>
1 = Background is drawn to screen, and PPU bus is active<br/>
0 = Background is not drawn. If both '''SPR''' and '''BKGD''' are clear, then the PPU bus is inactive
|-
| bit 2 || '''SPRCLIP''': Draw sprites in leftmost 8 pixels<br/>
1 = Sprites are visible in leftmost 8 columns<br/>
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<br/>
1 = Backgrounds are visible in leftmost 8 columns</br>
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<br/>
1 = All PPU palette reads for any purpose (rendering or via PPUDATA) are masked with $30.<br/>
0 = PPU palette reads function as normal, specifying any value of the normal palette
|}
===REGISTER: PPUSTATUS: PPU status===
{| class="tabular"
|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 || colspan=6| || bit 0
|}
{| style="border:1px solid black;"
| '''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
|}
{|
| style="width:4em;"|bit 7 || '''VBL''': Vertical blanking<br/>
1 = An NMI would occur (or has occured)<br/>
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<br/>
1 = A pixel in sprite 0 has overlaid some opaque pixel from the background<br/>
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<br/>
1 = More than 8 sprites attempted to be rendered on a scanline (but see [[Errata]])<br/>
0 = No scanline has had more than 8 sprites on it this frame.
|-
| bit 4-0 || '''Unimplemented''': Read as PPU's open bus<br/>
|}
|}

Revision as of 22:18, 15 February 2015

Just so I can find these again easily:


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

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 SPR BKGD 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 SPR: Sprite rendering enable

1 = Sprites are drawn to screen, and PPU bus is active
0 = Sprites are not drawn

bit 3 BKGD: Background rendering enable

1 = Background is drawn to screen, and PPU bus is active
0 = Background is not drawn. If both SPR and BKGD 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
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