What I have gathered so far:
- A12 is high when PPU reads/writes from/to addresses that have bit #12 set (0x1000-0x1fff, 0x3000-0x3fff), and low for all other addresses
- A12 must remain low for a while for rising edges to have an effect on the counter.
- Writing to $2006 is reflected on the address lines, even though no memory access happens.
What does the part between the parentheses mean? What is M2?The MMC3 scanline counter is based entirely on PPU A12, triggered on rising edges (after the line remains low for two falling edges of M2).