CPU variants
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Beyond the well-studied 2A03G, we know of the following CPU revisions, both made by Ricoh and other manufacturers:
| RP2A03 | M2 duty cycle is 17/24 instead of 15/24 [1]. Lacks tonal noise mode. Has broken and disabled programmable interval timer on-die. Pin 30 connects to nothing. Other differences? |
| RP2A03E | Subtle DMC DMA timing differences[2]. Pin 30 causes a crash (maybe?) |
| RP2A03G | reference model |
| RP2A03H | no known differences |
| RP2A04 | Not actually a CPU at all, just a jumper in a 40-pin PDIP |
| RP2A07 | input clock divider is 16. M2 duty cycle is 19/32 [3]. Changes to noise, DPCM, frame timer tables. Fixed DPCM RDY address bus glitches. Pin 30 connects to 6502 /RDY input. |
| RP2A07A | no known differences relative to 2A07letterless |
| MG-P-501 | Micro Genius-made clone. No specifics known. |
| UA6527 | UMC-made clone of 2A03G. Has swapped pulse channel duty cycles. |
| UA6527P | UMC-made clone of 2A03G for compatibility with NTSC software in PAL countries. input clock divider is 15. Otherwise believed same as 6527.
Two revisions exist: before mid-1990 (which has UMC logo on left) and after-mid-1990 (which has UMC logo on top). It is said that old UMC CPU has broken DMC reader function [4]. Addidionally it has input clock divider equals to 16 in contrary to the 15 present in newer one, that would explain why some games work differently (for example: CodeMasters' titles)
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| UA6540 | UMC-made clone of 2A07 [5]. Has swapped pulse duty cycles. |
| UM6557 | Believed to be a 100% duplicate of UA6527, for use in SECAM regions. |
| UM6561xx-1 | NES-on-a-chip for NTSC. Revisions "xx" AF, BF, CF, F known. Earlier revisions (which?) CPU half believed identical to UA6527; later revisions correct pulse channel duties. |
| UM6561xx-2 | NES-on-a-chip for PAL-B. Revisions "xx" AF, BF, CF, F known. Earlier revisions (which?) CPU half believed identical to UA6527P; later revisions correct pulse channel duties.
"AF" revision pulse wave duties observed to be same as 2A03. |
| T1818 | ??-made NES-on-a-chip, NTSC timing. Believed to exist, but evidence currently scant. |
| T1818P | ??-made NES-on-a-chip[[6]. Requires external 2 KiB RAMs for CPU and PPU. Swapped pulse duty cycles. |
| TA-03N | ??-made clone of 2A03G. Pin 30 selects input clock divider? |
| TA-03NP | ??-made clone of 2A03G for NTSC compatibility in PAL countries. Input clock divider is 15. |
| TA-03NP1 | ??-made clone of 2A03G for NTSC compatibility in PAL countries. Input clock divider is 15. Fixed DPCM problems? |
| PM03 | Gradiente-made clone of 2A03G. [7] |
| KC-6005 | Found in MT777-DX famiclone, behaves exactly like UA6527P
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If you know of other differences or other revisions, please add them!
