Re: [stella] What I've got so far

Subject: Re: [stella] What I've got so far
From: gentlben@xxxxxxxxxxxx
Date: Sat, 10 Jul 1999 05:40:54 -0700
> Forgive me for asking so many questions, but you guys explain things so
> much clearer than the Stella manual.

yeah, there are some things that the stella manual
doesn't explain very well...just wait until you begin
to work on horizontal positioning of the players and
missiles and ball!  <evil laughter>...but seriously,
it is still nice to have the stella document :)

> So I would start the program with:
> LDA #$02
> Because this hex number, when tranlated to binary, is 00000010 and bit
> 1 at memory location $0000 starts VSYNC, and I next:
> STA $0000
> Once that is done, I can put a couple of commands in, to blank out some
> memory or something.  After a few commands, I would:
> WSYNC
> Then I can put a couple of other things here if I want, or just leave
> it blank and immediately:
> WSYNC
> Then I do whatever it was again and:
> WSYNC
> That will make the third scanline for the VSYNC.  I then:
> LDA #$00
> STA $0000
> Which turns off the VSYNC and then I start working on the VBLANK area,
> right?  (Not to repeat everything gentlben wrote, I just want to make
> sure I have the logic right.)

writing $02 to the register VSYNC would begin vertical
sync, yes.  but may i suggest just using two zeroes instead
of four when writing to the TIA registers, since they are
all within $0000-$00FF?  and to start writing VBLANK
you turn it on the same way you turned on VSYNC, but
this time, write to $01.

also, if you want to do stuff like blank out memory or
other important initialization things (like setting
flags and clearing registers), ive found that most
programmers simply do that at the beginning of the
program, then when all that is done, begin VSYNC and
VBLANK...but during VSYNC and VBLANK, you have about
40 scanlines worth of free cycles to do whatever you
wish...but if you dont want to do anything at all, just
WSYNC through the scanlines...

btw, ive been trying to get the stella mailing list to
show me as something other than gentlben...i sign almost
all the email i write to this list with 'dee' :P

> So VBLANK just sends out whatever color is in the background register
> at that time, huh?  Could come in very handy.

but VBLANK wont display anything on the screen...
not the background or the playfield or any of the
neat little moveable objects. you have to actually
get to the picture lines before anything will be
shown...at which point VBLANK is turned off and
you begin to really code :)

> I'll have you know if you shoot me with a drugged dart, I'll...well,
> I'll be very happy, but that's beside the point!  ;-)

true :) i know there are times i could have used a nice
quiet snooze but couldnt get one...

dee


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