PPU variants
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Beyond the well-studied 2C02G, we know of the following PPU revisions, both made by Ricoh and other manufacturers:
| RP2C02 | Extremely rare. Likely only a few thousand made. (pictures not archived)
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| RP2C02A | Sometimes erroneous sprite pixels appear in X=255. Some modern PCBs generate almost exclusively glitchy pattern fetches. PPUMASK and PPUCTRL seem to be entirely asynchronous, and writes to PPUMASK can disable rendering for one pixel with the commensurate bugs resulting.
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| RP2C02B | Sometimes erroneous sprite pixels appear in X=255.
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| RP2C02C | 
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| RC2C02C | In ceramic package. [1]
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| RP2C02D | 
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| RP2C02D-0 |  
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| RP2C02E |  
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| RP2C02E-0 | In this and all previous revisions, OAMDATA and palette RAM are not readable.
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| RP2C02G-0 | Writes to OAMADDR cause corruption of OAM. Leaving OAMADDR at a value of 8 or greater causes OAM corruption when rendering starts. Particularly susceptible to reflections causing OAM corruption, fixed by putting series resistors between the CPU and the cartridge ROM.
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| RP2C02H-0 | Thought have to have fixed some of the glitches in the 2C02G
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| RP2C03B | RGB PPU. Color emphasis bits set the corresponding channel to full brightness. Otherwise believed identical to 2C02B. OAMDATA and PPU palette are not readable.
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| RP2C03C | RGB PPU. Believed to be same core as 2C02C.
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| RC2C03B | Tweaked palette; otherwise believed identical to RP2C03B.
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| RC2C03C | Believed identical to RP2C03C.
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| RP2C04 0001 | Scrambled palette and new colors, otherwise like 2C03C.
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| RP2C04 0002 | "
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| RP2C04 0003 | "
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| RP2C04 0004 | "
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| RC2C05-01 | PPUCTRL and PPUMASK swap locations. Five LSBs of PPUSTATUS return a constant. Otherwise like 2C03.
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| RC2C05-02 | " |
| RC2C05-03 |  same as above
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| RC2C05-04 |  same as above
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| RC2C05-99 | An RGB PPU with RP2C02E behavior: OAM and palettes are unreadable, but OAM corruption added in revision E is present. PPUSTATUS behavior is normal (the low 5 bits are PPU open bus). Grayscale is normal (palette & $30). Uses 2C02 timing (a dot is skipped every other frame), unlike other RGB PPUs. The palette and emphasis behavior match other RGB PPUs. Used in the Famicom Titler. (picture of Titler PCBs)
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| RP2C07 | PAL-B PPU. Vblanking is 71 scanlines long. OAM evaluation can never be fully disabled. Red/green color emphasis swapped. OAMADDR works correctly, not corrupting OAM contents.
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| RP2C07-0 | 
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| RP2C07A-0 | Some subtle differences in PPU that make this work better with Kevtris's HDNES, but otherwise believed identical to 2C07.
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| UA6528 | UMC-made clone of 2C02E (or something earlier) [2]
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| UA6528P | UMC-made variant for PAL-N (Argentina) [3] System crystal is 21492337.5 Hz (exactly 6×229.2516×15625)
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| UA6538(P??) | UMC-made variant for playing NTSC games in PAL countries. Emits PAL-B video. Vblank interrupt intentionally emitted 50 scanlines later than 2C07. Video DAC is brighter and more saturated (how so?). See also Clock rate.
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| UA6541 | UMC-made clone of 2C07 [4]
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| UA6548 | UMC-made variant for PAL-M (Brazil) System crystal is 21453671… Hz (exactly 6×227.25×4500000÷286)
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| UM6558 | UMC-made variant of UA6538 for SECAM countries. Emits 8-bit "Color Data" digital bus, for conversion into SECAM by UA6559 IC. Color palette noticeably off. System crystal is 21312500 Hz (exactly 4×341×15625). Maybe supports both 50 and 60 Hz operation?
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| UM6561xx-1 | UMC-made NES-on-a-chip for NTSC. PPU half believed to be mostly identical to UA6528. Revisions "xx" F, AF, BF, CF known.
Emphasis is much stronger than on UA6528 and official PPUs. |
| UM6561xx-2 | UMC-made NES-on-a-chip for PAL-B. PPU half believed to be mostly identical to UA6538. Revisions "xx" F, AF, BF, CF known.
AF revision has graphical and timing glitches in Prince of Persia perhaps caused by sprite 0 hit being missed for reasons not yet understood. F and BF revisions are not affected. Emphasis is much stronger than on UA6538 and official PPUs.
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| TA-02N | ??-made die-mask clone of 2C02G, despite the "6528" label.[5] Chip underside also has two codes of currently unknown purpose.
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| TA-02NP | ??-made PPU, Dendy compatible (not a 6538 clone). Pins 14-17 are background color in, like normal 2C03[6]
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| TA-02NPB | ??-made PPU, "NTSC for PAL-B" (NPB) Dendy-compatible. Has a unique video switching capability shared between it and other TA-02NPx chipsets, as well as the WDL chipset.
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| TA-08 | ??-made PPU, Second source alternative to UM6558. Color Data bus bit-reversed?
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| MG-N-502 | 
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| MG-P-502 | Micro Genius / TXC. Die shot matches UA6538.
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| 1818N | ??-made NES-on-a-chip, NTSC timing.
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| 1818P | SiS-made[7]] NES-on-a-chip.[8]. Requires external 2KiB RAMs for CPU and PPU. UA6538 timing.
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| PM02-1 | Gradiente-made variant for PAL-M (Brazil). [9]
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| VT01 | V.R.Tech-made clone of UA6561. Only seen as chip-on-board. Supports composite out; RGB out; or 2bpp STN LCD, either greyscale or red/cyan checkerboard, 240 px wide, 80/120/160/240px tall. The chip was extended significantly in VT02 and newer NOACs. |
| GS87008 | (Goldstar??)-made NTSC clone [10]
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| KC-6078 | Found in MT777-DX famiclone, behaves exactly like UA6538
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| 6022 | ??-made NTSC clone. Details unknown.
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| 2010 | 
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| 2A02E | 
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| 02 | 
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| GT-01 |  In PLCC
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| HA6538 | 
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| 6538U-8 | 
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| 6538A |  
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| 6528 | WDL made chip. NTSC timing. Palette like RP2C02.
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If you know of other differences or other revisions, please add them!
