Aha.. Another two questions:

1.- How many CPU cycles are runned during the VBlank?

2.- There's something I don't understand yet. In NTSC render starts at the 17th scanline (first and last 16 lines are not shown) and in PAL render starts at the 9th scanline (first and last 8 lines are not shown).. But I see everywhere that this occurs on the scanline 20 (all emus & posts I've seen clear VBlank flag at this point..). What am I missing?

Thanks again.