CPU variants

Beyond the well-studied 2A03G, we know of the following CPU revisions, both made by Ricoh and other manufacturers:

Official (NTSC)

Part	Picture	Notes
RP2A03		M2 duty cycle is 17/24 instead of 15/24 [1]. Lacks tonal noise mode. APU Frame Counter not restarted on reset. Has broken and disabled programmable interval timer on-die. Pin 30 connects to nothing. Other differences?
RP2A03E		Pin 30 is /RDY - combined with internal signals before feeding to internal 6502 +RDY.
RP2A03G		Reference model. Pin 30 enables a CPU test mode. Later runs introduced a DMC DMA bug [2].
RP2A03H		No known differences from late RP2A03G.
RP2A04		Not actually a CPU at all, just a jumper in a 40-pin PDIP. Used in place of CPUs in Vs. System boards (and thus with NTSC timing).

Official (PAL)

Part	Picture	Notes
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

Unofficial

Part	Picture	Notes
MG-N-501
MG-P-501		Micro Genius-made clone. Die has the same (UMC) © Ⓜ B6167F marking as a UA6527P.
UA6527		UMC-made clone of 2A03G. Has swapped pulse channel duty cycles. Input clock Divider is 12.
UA6527P	UMC-made clone of 2A03G for compatibility with NTSC software in PAL countries. Different input clock divider. Still has swapped pulse channel duty cycles. Otherwise believed same as 6527. One revision has (UMC) © Ⓜ B6167F 1989 09 on the die. DMC status bit is cleared 1 APU cycle later than on RP2A03 CPUs. The cause is not known. This changes the timing for DMC DMA implicit-stop glitches (the sample must be started 1 APU cycle earlier to trigger the glitches), and it is suspected that it delays DMC IRQ by 1 APU cycle. Noise channel is slightly louder than others.
		Runs hot. Revisions without "-" in the date stamp have a ÷16 CPU divider, like 6540 and 2A07
		Runs hot. Revisions with "-" in the date stamp have a ÷15 CPU divider
		Runs cooler
UA6527PQ
UA6540		UMC-made clone of 2A07 [4]. Has swapped pulse duty cycles. Subsequent research implies this is identical to the early 6527P - NTSC tuning tables, ÷16 CPU divider. [5]
UM6547		Believed to be a 100% duplicate of UA6527, for use in PAL-M region.
UM6557		Believed to be a 100% duplicate of UA6527, for use in SECAM regions.
UM6561xx-1	No Picture	NES-on-a-chip for NTSC. Revisions "xx" F, AF, BF, CF known.
UM6561xx-2		NES-on-a-chip for PAL-B. Revisions "xx" F, AF, BF, CF known. F and AF revision pulse wave duty cycles match RP2A03, and DMC status bit is cleared 1 APU cycle later than on RP2A03 CPUs. AF revision observed to have incorrect ASR #imm ($4B) behavior, but other stable illegal instructions work properly.
1818N		??-made NES-on-a-chip, NTSC timing.
T1818P		??-made NES-on-a-chip[[6]. Requires external 2 KiB RAMs for CPU and PPU. Swapped pulse duty cycles. DMC status bit is cleared 1 APU cycle later than on RP2A03 CPUs.
TA-03N		??-made die-mask clone of 2A03G. Chip underside also has two codes of currently unknown purpose. Pin 30 activates CPU Test Mode like on 2A03G. Clock Divisor is 12. Illegal opcodes are the same. Early 1991 dated chips are reported to have problems with APU DMC playback, but this was corrected in 1992 onward. Runs hot.
TA-03NP		??-made clone of 2A03G for NTSC compatibility in PAL countries. Input clock divider is 15? But not this one, this input clock divider is 12.
TA-03NP1		??-made clone of 2A03G for NTSC compatibility in PAL countries. Input clock divider is 15. Fixed DPCM problems? Correct pulse channel duties. Noise channel is slightly louder than others. DMC status bit is cleared 1 APU cycle later than on RP2A03 CPUs.
PM03		Gradiente-made clone of 2A03G. [7]
GS870007		(Goldstar??)-made clone of 2A03 - has functioning decimal mode? [8]
KC-6005		Found in MT777-DX famiclone, behaves exactly like UA6527P
6005B
2011
“2A03E”		Both with and without USC insignia
KP2B03E
6527-21
6527P
HA6527P
6527P-SS-P03
6527UP-8
6527AP
SL/WH6527AP
SNC6527P
XYZ-6783		Lacks tonal noise mode like original RP2A03, but resets APU Frame Counter on console reset like 2A03E/2A03G. Otherwise behaves like letterless RP2A03.
6538N		??-made CPU, despite the part number being similar to UMC PPU. Has inverted duty cycles like UA6527. DPCM works.
8Z01N

If you know of other differences or other revisions, please add them!

See also

• PPU variants
• https://forums.nesdev.org/viewtopic.php?p=45889#p45889
• https://forums.nesdev.org/viewtopic.php?t=23916 (More Info on CPU Clones)
• https://forums.nesdev.org/viewtopic.php?t=23682 (Lots of Images and die-shots)