carlsson wrote:Unless I'm totally confused, it means $9004 will become 0..4 twice per frame in NTSC, 0..55 in PAL [...]
There's no ambiguity here: $9004 contains bits 1..8 of the current raster line, i.e. there's a granularity of two raster lines. Bit 0 is stored within bit 8 of $9003.
Leeeeee wrote:Line 27 waits for near the end of frame so that the effect doesn't retrigger prematurely.
I can't see how it could retrigger (other than basic code being executed within the same two rasterlines, but it's not the case). Am I missing something?