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No. I didn't mention that because I didn't think it was relevant. In test mode, reads from the entire region $4000-$401F are from the special internal bus, instead of only reads from $4015. Oh, snap. Well, I've got a DP ram between the 2A03 and the MCU, so with a few more cycles, I can fetch things...

I have a question about the 2A03's bus signals: Do these always behave the same way for internal register accesses as they do for external accesses? The only thing that does not show up externally with the 2A03 is reads from $4015, which happens from a special 2A03-internal bus. For the 2C02, what ...

Welcome. I think everything shows up on the CPU bus. My understanding is that the only thing hidden from cartridges are accesses to the PPU at $3F00-$3FFF. Ok, that's very good to know. *Crosses a few doomed ideas off the list!* For context, I'm actually working on vNext of this thing . To the impl...

(First post! Woo-hooo!!) I have a question about the 2A03's bus signals: Do these always behave the same way for internal register accesses as they do for external accesses? For e.g.: Does writing something to $4000 cause that something to appear on D[7:0], $4000 to appear on A[15:0], R/W to go low?...