3 replies to this topic

[Tom]

one thing i don't really understand is how you get all the vertical timing stuff *correct*:

according to the stella manual, you do it like this:

- generate 3 lines of vsync, by setting VSYNC to 2 for the duration of 3 scanlines
- generate 37 lines of vblank, by setting VBLANK to 2 for the duration of 37 lines
- draw your image (192 or 242 lines)
- 30 lines of overscan

what confuses me is the vblank stuff: in the tutorials, VBLANK is set to 01000001b during overscan, vsync and vblank period. so what's correct now ? or doesn't it matter at all ? and why is bit 6 of VBLANK set ?

[Thomas Jentzsch]

Tom said:

what confuses me is the vblank stuff: in the tutorials, VBLANK is set to 01000001b during overscan, vsync and vblank period. so what's correct now ? or doesn't it matter at all ? and why is bit 6 of VBLANK set ?

Bit 6 dumpes (resets) the paddles ports. So it is only necessary for paddle games, but there is no problem if you also set it for joystick games.

[EricBall]

See Session 13: Playfield Basics for my comments about the VBLANK control bits and some other comments about VBLANK usage.

[Tom]

EricBall: yeah, that cleared everything up, thanks