Re: [stella] 8K Cart question

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?


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