User:Ddribin/PPU Sandbox: Difference between revisions

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== PPU Registers ==
= PPU Registers =
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== PPUCTRL ==
== PPUCTRL: PPU Control Register ==


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Revision as of 15:02, 25 December 2009

PPU Registers

Address Register Function
$2000 #PPUCTRL PPU Control Register
$2001 PPUMASK PPU Mask Register
$2002 PPUSTATUS PPU Status Register

PPUCTRL: PPU Control Register

Bit 7 6 5 4 3 2 1 0
$2000 NMI MSS SSZ BPT SPT VDN NTA1 NTA0
Read/Write W W W W W W W W
Initial Value X X X X X X X X
Bit 7 - NMI: NMI Enable

Setting NMI to one causes an NMI to be generated at the start of the vertical blanking interval

Bit 6 - MSS: Master/Slave Enable

Has no effect on the NES.

Bit 5 - SSZ: Sprite Size

0: 8x8; 1: 8x16

Bit 4 - BPT: Background Pattern Table

Background pattern table address (0: $0000; 1: $1000)

Bit 3 - SPT: Sprite Pattern Table

Sprite pattern table address for 8x8 sprites (0: $0000; 1: $1000)

Bit 2 - VDN: VRAM Increment Down

VRAM address increment per CPU read/write of PPUDATA (0: increment by 1, going across; 1: increment by 32, going down)

Bits 1, 0 - NTA1 and NTA0: Base Nametable Address
NTA1 NTA0 Base VRAM Address
0 0 $2000 (Nametable 0)
0 1 $2400 (Nametable 1)
1 0 $2800 (Nametable 2)
1 1 $2C00 (Nametable 3)

PPUSTATUS - The PPU Status Register

Bit 7 6 5 4 3 2 1 0
$2001 INB ING INR SPR BGR SPC BGC GRY
Read/Write W W W W W W W W
Initial Value X X X X X X X X
Bit 7 - INB: Intensify Blues
Bit 6 - ING: Intensify Greens
Bit 5 - INR: Intensify Reds
Bit 4 - SPR: Sprite Render Enable
Bit 3 - BGR: Background Render Enable
Bit 2 - SPC: Sprite Clip
Bit 1 - BGC: Background Clip
Bit 0 - GRY: Grayscale Enable

CA65 Definitions

.define bit2mask(bitnum) (1 << bitnum)
.define bits2mask(bits, bitnum) (bits << bitnum)

        ;; PPU Registers
        ppuctrl         := $2000
        ppumask         := $2001

        ppuctrl_nmi = bit2mask(7)
        ppuctrl_mss = bit2mask(6)
        ppuctrl_ssz = bit2mask(5)
        ppuctrl_bpt = bit2mask(4)
        ppuctrl_spt = bit2mask(3)
        ppuctrl_vdn = bit2mask(2)
        ppuctrl_nta1 = bit2mask(1)
        ppuctrl_nta0 = bit2mask(0)

        ppuctrl_nta_2000 = bits2mask(%00, ppuctrl_nta0)
        ppuctrl_nta_2400 = bits2mask(%01, ppuctrl_nta0)
        ppuctrl_nta_2800 = bits2mask(%10, ppuctrl_nta0)
        ppuctrl_nta_2c00 = bits2mask(%11, ppuctrl_nta0)
        
        ppumask_inb = bit2mask(7)
        ppumask_ing = bit2mask(6)
        ppumask_inr = bit2mask(5)
        ppumask_spr = bit2mask(4)
        ppumask_bgr = bit2mask(3)
        ppumask_spc = bit2mask(2)
        ppumask_bgc = bit2mask(1)
        ppumask_gry = bit2mask(0)