Re: [stella] A new way to bankswitch

Subject: Re: [stella] A new way to bankswitch
From: "Kroko" <Nil.Krokodil@xxxxxxx>
Date: Wed, 9 Mar 2005 17:50:38 -0500
Hi Fred !

> I thought about that.  It does depend on how fast the hardware operates.
> There is only one cycle between $FFF8 and $FFF9 accesses.  Standard logic
> chips should be more than fast enough for this, it's just that the
> hardware
> I've seen uses a 0.1 uF capacitor to filter out glitches, and this cap may
> slow down the switching enough to cause this to not work.

I don't agree on that. Look at the timing diagram for an LDA $FFF8:

 #  address R/W description
       --- ------- --- ------------------------------------------
        1    PC     R  fetch opcode, increment PC
        2    PC     R  fetch low byte of address, increment PC
        3    PC     R  fetch high byte of address, increment PC
        4  address  R  read from effective address

When the LDA $FFF8 is executed, you only have the effective adress
on the bus for one processor cycle. So If the bankswitching hardware does
not switch, if it sees a valid adress for one cycle, it will simply not work
at all :-)

And the 0.1 5F Cap is good for about 3005s delay. I think I calculated that
a while ago.
Don't know the exact value, but it is in that range. It should switch !


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