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 command. 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 ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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