>After VBLANK and before beginning to draw the screen in Nick's HtDaP, I
>_think_ I have #44 times 64 clock counts, or 2816 total clocks for game
>calcs, etc. That would be about 938.7 machine cycles if I believe page 2
>of my fancy Stella Programmer's Guide where it says "3 CLOCK COUNTS PER
>MACHINE CYCLE". Now that only comes to 12 lines and change (938.7 div
>76) worth of time for game calculations... Since there are 37 lines of
>VBLANK, that seems a bit small. What did I do wrong?
There's two kinds of clock counts. The 6507 CPU clock runs at 1.19 MHz;
the graphics clock runs at 3.57 MHz, or three times the CPU speed. In
other words, three pixels get drawn on the screen during one CPU cycle.
Your #44 times 64 clock counts is correct... the timer uses CPU clocks, not
graphics clocks, so it's 2816 machine cycles which is (div 76) 37-some-odd
lines.
>Secondly, there isn't anything about the overscan that's tricky, is
>there? Meaning I can treat that exactly like it's 30 lines of normal
>screen scan, correct? Is the gun still shooting the screen? Could I put
The gun is always shooting as long as VBLANK holds a nonzero value. You
can treat it as normal screen scan, yes. The only catch there is that
after 5 to 25 lines of overscan (the exact number depends on the TV set),
the electron gun is no longer pointing at the phosphored screen - it's
aiming at the plastic below there (or wood if you have a really old set),
so anything you draw won't show up.
Same holds for vertical blank - you can start drawing before 37 lines have
passed and it'll show up higher on the screen, but too high and it'll be
off the top of the screen.
>two 1702 monitors together and get a really nice long screen and make
>Millipede the right size? (Just kidding about the last question, of
>course)
I don't think so :)
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