User:Ddribin/PPU Sandbox

PPU Register Overview

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)