Re: [stella] FE Bankswitching

Subject: Re: [stella] FE Bankswitching
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Fri, 28 Feb 2003 21:12:06 +0100
Do I totally misunderstand this, or could it be like this.
Does anybody know how to interpret (predecrement S?)

No, you got everything right. I don't think the address
changes between the read and write access to the stack.
The "predecrement S?" probably only means that no-one
really knows what this step is needed for in the JSR

So to handle FE bankswitching, you only need to wait
for two consecutive accesses to the stack area ($0100-
$01FF). During the next cycle the high byte of the
destination address will be read (from stack for RTS
and from ROM for JSR), so that you can take data bit
D5 from there and put it on A12 on your ROM chip.
You must invert D5, because the emulator ROM images
have the bank compiled for $F000-$FFFF before the
bank compiled for $D000-$DFFF.

I have no idea how long you'd have to wait between
finding the second stack access and evluating D5.
Maybe one of the hardware experts on this list can
help here.

Ciao, Eckhard Stolberg

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Current Thread
  • [stella] FE Bankswitching
    • Kroko - Wed, 26 Feb 2003 13:14:41 -0500 (EST)
      • Adam Wozniak - Wed, 26 Feb 2003 15:48:07 -0500 (EST)
        • Kroko - Wed, 26 Feb 2003 16:54:58 -0500 (EST)
          • Eckhard Stolberg - Fri, 28 Feb 2003 15:47:05 -0500 (EST) <=
          • Adam Wozniak - Fri, 28 Feb 2003 20:02:58 -0500 (EST)
          • Eric Ball - Fri, 28 Feb 2003 22:00:29 -0500 (EST)
          • Kroko - Fri, 28 Feb 2003 22:16:46 -0500 (EST)