Re: [stella] The mother of all bankswitching trickery :-)

Subject: Re: [stella] The mother of all bankswitching trickery :-)
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Mon, 9 Dec 2002 13:55:30 +0100
> Not quite.  The cartridge connector has all 13 address lines (A0-A12), but
> typically A12 is used as a positive chip select or output enable.  Thus FE
> bankswitching is possible, because the cartridge can monitor all memory
> accesses.

Not quite. ;-) In FE bankswitching A13 is used to identify the
two banks. Since this line isn't brought out of the 6507, the
FE bankswitching logic waits for two consecutive accesses to
this stack. Only JSR/RTS (and BRK/RTI) can do that. At the second
access the high byte of the return address is either pushed onto
or pulled from the stack. This is where the bankswitching logic
finds out which bank need to be mapped in.

Ciao, Eckhard Stolberg

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