User:Ddribin/PPU Sandbox: Difference between revisions

Latest revision as of 22:09, 5 December 2010

PPU Register Overview

The PPU exposes only eight memory-mapped registers to the CPU. These nominally sit at $2000 through $2007 in the CPU's address space, but because they're incompletely decoded, they're mirrored in every 8 bytes from $2008 through $3FFF, so a write to $3456 is the same as a write to $2006.

PPU Registers
Address	Name	(Alt. Names?)	Function
$2000	PPUCR1	PPUCTRL PCR	PPU Control Register 1
$2001	PPUCR2	PPUMASK PPUMR PMR	PPU Control Register 2
$2002	PPUSR	PPUSTATUS PSR	PPU Status Register
$2003	OAMAR	OAMADDR OAR	OAM Address Register
$2004	OAMDR	OAMDATA ODR	OAM Data Register
$2005	PPUSCR	PPUSCROLL PSCR	PPU Scroll Register
$2006	PPUAR	PPUADDR PAR	PPU Address Register
$2007	PPUDR	PPUDATA PDR	PPU Data Register
$4014	OAMDMA	ODMA	OAM DMA

PPUCR1: PPU Control Register 1

Bit	7	6	5	4	3	2	1	0
$2000	NMIE	MSE	SSZ	BPT	SPT	VDN	NTA1	NTA0
Read/Write	W	W	W	W	W	W	W	W
Initial Value	0	X	0	0	0	0	0	0

Bit 7 - NMIE: NMI Enable

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

Bit 6 - MSE: 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 1 and 0

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)

PPUCR2: PPU Control Register 2

Bit	7	6	5	4	3	2	1	0
$2001	INB	ING	INR	SRE	BRE	SCD	BCD	GSE
Read/Write	W	W	W	W	W	W	W	W
Initial Value	0	0	0	0	0	X	X	0

Bit 7 - INB: Intensify Blues

Intensify blues and darken other colors.

Bit 6 - ING: Intensify Greens

Intensify greens and darken other colors.

Bit 5 - INR: Intensify Reds

Intensify reds and darken other colors.

Bit 4 - SRE: Sprite Render Enable

Enable sprite rendering.

Bit 3 - BRE: Background Render Enable

Enable background rendering.

Bit 2 - SCD: Sprite Clip Disable

Control sprite clipping in leftmost 8 pixels of screen (0: clip; 1: display).

Bit 1 - BCD: Background Clip Disable

Control background clipping in leftmost 8 pixels of screen (0: clip; 1: display).

Bit 0 - GSE: Grayscale Enable

0: normal color; 1: AND all palette entries with 0x30, effectively producing a monochrome display; note that colour emphasis STILL works when this is on!

PPUSR: PPU Status Register

Bit	7	6	5	4	3	2	1	0
$2002	VBL	S0H	SOV	---	---	---	---	---
Read/Write	R	R	R	R	R	R	R	R
Initial Value	X	0	X	X	X	X	X	X

Bit 7 - VBL: Vertical Blank

Bit 6 - S0H: Sprite 0 Hit

Bit 5 - SOV: Sprite Overflow

Bits 4..0 - Res: Reserved

CA65 Definitions

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

        ;; PPU Registers
        ppucr1 := $2000
        nmie = bit2mask(7)
        mse  = bit2mask(6)
        ssz  = bit2mask(5)
        bpt  = bit2mask(4)
        spt  = bit2mask(3)
        vdn  = bit2mask(2)
        nta1 = bit2mask(1)
        nta0 = bit2mask(0)

        nta_2000 = bits2mask(%00, nta0)
        nta_2400 = bits2mask(%01, nta0)
        nta_2800 = bits2mask(%10, nta0)
        nta_2c00 = bits2mask(%11, nta0)

        ppucr2 := $2001
        inb = bit2mask(7)
        ing = bit2mask(6)
        inr = bit2mask(5)
        sre = bit2mask(4)
        bre = bit2mask(3)
        scd = bit2mask(2)
        bcd = bit2mask(1)
        gse= bit2mask(0)

        ppusr := $2002
        vbl = bit2mask(7)
        s0h = bit2mask(6)
        sov = bit2mask(5)

        oamaddr := $2003
        oamdata := $2004
        ppuscroll := $2005
        ppuaddr := $2006
        ppuaddr := $2007
        oamdma := $4014

@@ Line 8: / Line 8: @@
 ! Address !! Name !! (Alt. Names?) !! Function
 |-
-| $2000 || [[#PPUCTRL|PPUCTRL]] || PPUCR PCR ||  PPU Control Register
+| $2000 || [[#PPUCR1|PPUCR1]] || PPUCTRL PCR ||  PPU Control Register 1
 |-
-| $2001 || [[#PPUMASK|PPUMASK]] || PPUMR  PMR || PPU Mask Register
+| $2001 || [[#PPUCR1|PPUCR2]] || PPUMASK PPUMR  PMR || PPU Control Register 2
 |-
-| $2002 || [[#PPUSTATUS|PPUSTATUS]] || PPUSR PSR || PPU Status Register
+| $2002 || [[#PPUSR|PPUSR]] || PPUSTATUS PSR || PPU Status Register
 |-
-| $2003 || OAMADDR || OAMAR OAR || OAM Address Register
+| $2003 || OAMAR || OAMADDR OAR || OAM Address Register
 |-
-| $2004 || OAMDATA || OAMDR  ODR || OAM Data Register
+| $2004 || OAMDR || OAMDATA ODR || OAM Data Register
 |-
-| $2005 || PPUSCROLL || PPUSCR PSCR || PPU Scroll Register
+| $2005 || PPUSCR || PPUSCROLL PSCR || PPU Scroll Register
 |-
-| $2006 || PPUADDR || PPUAR PAR || PPU Address Register
+| $2006 || PPUAR || PPUADDR PAR || PPU Address Register
 |-
-| $2007 || PPUDATA || PPUDR PDR || PPU Data Register
+| $2007 || PPUDR || PPUDATA PDR || PPU Data Register
 |-
 | $4014 || OAMDMA || ODMA || OAM DMA
 |}
-== <span id="PPUCTRL">PPUCTRL</span>: PPU Control Register ==
+== <span id="PPUCR1">PPUCR1</span>: PPU Control Register 1 ==
 {| class="wikitable" style="text-align:center;" border="1" cellspacing="0" cellpadding="3"
@@ Line 75: / Line 75: @@
 |}
-== <span id="PPUMASK">PPUMASK</span>: PPU Mask Register ==
+== <span id="PPUCR2">PPUCR2</span>: PPU Control Register 2 ==
 {| class="wikitable" style="text-align:center;" border="1" cellspacing="0" cellpadding="3"
@@ Line 123: / Line 123: @@
 : normal color; 1: AND all palette entries with 0x30, effectively producing a monochrome display; note that colour emphasis STILL works when this is on!
-== <span id="PPUSTATUS">PPUSTATUS</span>: PPU Status Register ==
+== <span id="PPUSR">PPUSR</span>: PPU Status Register ==
 {| class="wikitable" style="text-align:center;" border="1" cellspacing="0" cellpadding="3"
@@ Line 154: / Line 154: @@
          ;; PPU Registers
-         ppuctrl := $2000
+         ppucr1 := $2000
-         ppumask := $2001
+         nmie = bit2mask(7)
-         ppustatus := $2002
+        mse  = bit2mask(6)
+        ssz  = bit2mask(5)
+        bpt  = bit2mask(4)
+        spt  = bit2mask(3)
+        vdn  = bit2mask(2)
+        nta1 = bit2mask(1)
+        nta0 = bit2mask(0)
+        nta_2000 = bits2mask(%00, nta0)
+        nta_2400 = bits2mask(%01, nta0)
+        nta_2800 = bits2mask(%10, nta0)
+        nta_2c00 = bits2mask(%11, nta0)
+        ppucr2 := $2001
+         inb = bit2mask(7)
+        ing = bit2mask(6)
+        inr = bit2mask(5)
+        sre = bit2mask(4)
+        bre = bit2mask(3)
+        scd = bit2mask(2)
+        bcd = bit2mask(1)
+        gse= bit2mask(0)
+        ppusr := $2002
+        vbl = bit2mask(7)
+        s0h = bit2mask(6)
+        sov = bit2mask(5)
          oamaddr := $2003
          oamdata := $2004
@@ Line 163: / Line 190: @@
          ppuaddr := $2007
          oamdma := $4014
-        ppuctrl_nmie = bit2mask(7)
-        ppuctrl_mse = 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_sre = bit2mask(4)
-        ppumask_bre = bit2mask(3)
-        ppumask_scd = bit2mask(2)
-        ppumask_bcd = bit2mask(1)
-        ppumask_gse= bit2mask(0)
-        ppustatus_vbl = bit2mask(7)
-        ppustatus_s0h = bit2mask(6)
-        ppustatus_sov = bit2mask(5)
 </pre>