Subject: Re: [stella] some questions about the a2600 From: Chris Wilkson <ecwilkso@xxxxxxx> Date: Wed, 26 May 1999 11:31:54 -0400 (EDT) |
On Wed, 26 May 1999, Erik Mooney wrote: > >> > There are no interrupts on the 2600. > > > >but dont games usually have interrupt vectors stored at the end of the roms? > > They have vectors, yes, but they're not really for interrupts. The word > at address $FFFC is the address where the CPU will transfer control at > powerup, and the word at address $FFFA is the address where the CPU will > transfer control after hitting a BRK instruction. Actually, $FFFE is the BRK vector. MOst games simply use this vector to store 2 more bytes of data. But it seems like there was one that actually uses a BRK. Can anyone help out here? > They'll start displaying right at powerup (actually, the TV even before > powerup - static, or whatever happens to be on channel 3). But it doesn't > matter if it displays garbage or blankness for a few sixtieths of a second > before you get your VSYNCs rolling. Rolling VSYNCs? Hmmm...seems like that's self contradictory.... ;) Sorry, I'm just feeling silly today! :P > >well, i thought maybe i could use the f8 method of bankswitching by > >essentially > >creating two 4K files with code that could in essence be seperate roms, append > >one > >on top of the other, and then access locations $FFF9 and $FFF8 (since $1000 > >and $F000 are the same to the 6507) to switch back and forth between 4K > >sections... > >thats the way i see it...you think that would work? > > Sounds about like the standard method of writing bankswitched games. Yes, but if you want to implement this physically, a single rom is both simpler, and less power hungry. Just think of the chip as 2 separate 4k roms, selected by the A12 line. Actually, if you need a physical implementation, I know this guy.... :) -Chris -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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Re: [stella] a "pot" of confusion, Eckhard Stolberg | Thread | Re: [stella] some questions about t, gentlben |
Re: [stella] a "pot" of confusion, Erik Mooney | Date | [stella] remove, Han2000 |
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