I have in hand an original no-revision 2A03 CPU, from a PlayChoice 10 board. Once I am home I will be socketing the CPU and PPU on my NES, as well as getting an Everdrive N8. So, are there any interesting tests that I should run on this thing? There are mentions here and there of differences, the most notable being the APU ignoring the repeating noise bit, but apart from that I don't see much proper documentation of what changed in later revisions.
We don't really know what's changed. The only things I'm certain of are the lack of tonal noise and that pin 30 doesn't enable testing, but instead is either part of a crystal oscillator or somehow disables the clock.
It's conceivable that the un-read-ability of $2004 on the famicom is actually an artifact of the CPU instead of the PPU. And maybe the duty cycle of M2 differs between the 2A03 and 2A03G.
lidnariq wrote:
It's conceivable that the un-read-ability of $2004 on the famicom is actually an artifact of the CPU instead of the PPU.
Conceivable, but ludicrously unlikely - we know full well that everything visible at CPU $2000-$3FFF is internal to the PPU, so if changing the CPU made them behave differently, then the same would be true of
every MMC ever designed.
Unless it relates to analog characteristics of the motherboard traces between the two chips.
On an arcade repair forum, I've seen at least a couple people say that with the game VS TKO Boxing (AKA Ring King), that it works with original 2A03, but not with 2A03H (whether anyone has tried other revisions, I don't know). Something seems to be different. Either that, or it's more fake chips going around. I bought an H revision too from probably the same arcade parts supplier, but I think I had sent it in with the other CPUs to be decapped.
Could be related to whatever protection TKO Boxing uses (it's on a daughter-board, like all VS games with a mapper).
edit: BTW, I have an RP2A03E that came with my Playchoice, I could run any tests on it likewise, if it helps. Seems to be the same as the G revision as far as I can tell. My Playchoice is kinda broken down at the moment (power supply going out, maybe), but I've got the CPU in my front-loader.