Beyond the well-studied 2A03G, we know of the following CPU revisions, both made by Ricoh and other manufacturers:
|RP2A03||M2 duty cycle is 3/4 instead of 5/8. Lacks tonal noise mode. Has broken and disabled programmable interval timer on-die. Other differences?|
|RP2A03E||no known differences|
|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. Changes to noise, DPCM, frame timer tables. Fixed DPCM RDY address bus glitches. Other differences?|
|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 . 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)
|UA6540||UMC-made clone of 2A07 . 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[. Requires external 2 KiB RAMs for CPU and PPU. Swapped pulse duty cycles.|
|TA-03N||??-made clone of 2A03G|
|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. |
If you know of other differences or other revisions, please add them!