Subject: Re: [stella] Cart card edge connector From: "B. Watson" <atari@xxxxxxxxxxxxxx> Date: Mon, 3 Sep 2001 20:53:08 -0400 (EDT) |
On Mon, 3 Sep 2001, Kevin Horton wrote: > At 20:18 9/3/01 -0400, you wrote: > > >When I took the cart apart, the chip side of the board was facing up, so > >looking at the card edge with the chip side up, and looking at the pinout > >for the ROM chip (from, um, Kevin Horton's web site, I think?), I see that > >the chip's A11 line is wired to the card edge's A12 line, and the card edge's > >A11 line doesn't even have a pin... what gives? > > > >In fact, A0 thru A12 are present on the card edge connector... but this > >would allow for 8K carts, without bank switching. So is the FAQ wrong? > > > >I'm sure this has been discussed before on this list, I'm just trying to get > >clarification.. I *need* to understand this fully, before I break out the > >soldering iron. > > Simple. That's a 2K ROM, so it has no A11. That "A11" on the chip is > really the positive enable. If you connect it to A12, it will be enabled > when you are accessing the upper 4K of the total 8K address space. > D'oh! I was fooled by the fact that the rom dump of combat I have is 4k, but I see it's just 2 copies of the same 2k of data now... I had just assumed it was a 4k cart.. > A 4K chip has an A11, so you connect it to A11, and then A12 is still the > positive enable. (All EPROMs have negative enables, so you must use an > inverter (7404 or similar) to turn the positive enable into a negative one). > I knew about the inverters, got a pile of them. > You can only use the upper 4K of address space, since the lower 4K holds > the RAM, stack, TIA registers, etc. and is therefore unusable for code. > Oh yeah, I was being stupid... or overly optimistic :) Too bad the TIA, PIA, etc. decode as much address space as they do. If there weren't `mirrors' of them all over the first 4k, it could have been possible to have 6k or 7k carts, maybe. Too late to change that design decision now I guess :) Now, if only I could get my EPROMs to erase, I'd be ready to start soldering.. well, assuming I only wanted to use 2k of address space, since the missing pin on the combat cart means I don't get to use 4k... *sigh* I get to decide which of my priceless collection will be the next sacrificial victim. Maybe Pac-man, the Atari version sucks, and it's actually 4k, from looking at my rom dump of it (vector at $FFFC points to $F000) Brian --- If a trainstation is the place where trains stop, what is a workstation? - Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
Current Thread |
---|
|
<- Previous | Index | Next -> |
---|---|---|
Re: [stella] Cart card edge connect, Kevin Horton | Thread | Re: [stella] Cart card edge connect, Kevin Horton |
Re: [stella] Cart card edge connect, Kevin Horton | Date | Re: [stella] Cart card edge connect, Kevin Horton |
Month |