Subject: Re: [stella] 8K Cart question From: Mark De Smet <de-smet@xxxxxxxxxxxxxxx> Date: Tue, 7 Nov 2000 21:21:36 -0600 (CST) |
> with, I created a digital delay line by running the address change signal > through several inverters, and then anding the output of those inverters > together to form the bankswitch logic "clock". (All internal to the PLD.) Do you know what sort of delay time you have? > It occurs to me that this timing/glitch problem will also complicate life > for the carts containing ram or for 3F bankswitching as now you have to > know when the data lines are active and stable as well, which according to > the data sheet for the old Commodore nmos 6502, doesn't happen until the > second half of the clock cycle. And according to that data sheet the > address and data hold times after the end of the cycle are the same, so > grabbing the data lines right at the start of an address change seems like > a bad idea. > > So for something like this would you want two delays after a detection of a > change in address? One to tell you when to sample the address lines and > the other the data lines? As you may have guessed by my questions, I am slowly working on a bankswitch cart using programmable logic, and am looking for advice on solutions before I run into the problem. My current plan was to clock my logic at a high rate(at least 20mhz), then I could oversample, and do glitch detection etc on the address lines. This would also solve the problem of when to grab data for a write because you can wait until you get a stable address, then wait x amount of time before grabbing the data. Had you considered putting a clock in there for this, or are you just trying to do a simpler scheme? Are you making something just for yourself, or are you planning on posting info on the web such that people could replicate it? I think we really need bankswitch cart directions on the web as I don't believe there currently is any. That is half the reason I started to do one myself. Chris, Randy is currently using your design for bankswitching yes? Could you post schematics/code for it? Mark -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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