On Wed, 22 Apr 1998, Andre Fachat wrote: > Marko Mäkelä wrote: > > > Then explain me the $DE00/$DFFF trick of Marko :-) > > > > Explain it to me too. :-) By the way, a similar effect occurs also with > > the 1541 and with the VIC-20. Haven't you ever wondered why reading from > > a non-existing address returns the page number, e.g. reading from $20xx > > returns $20? Could it by any means have anything to do with the fact that > > the high-order byte of the address was on the data bus right before the > > read operation? :-) But why does it work? The VIC-20 and the 1541 have Also, the same thing occurs with the C128 in 2Mhz aka Fast mode. At least, if I unplug my Swiftlink. > > Does that work with indexed access as well? I mean, trying to read > something from a non-existant page with an overflow when adding the > index register. Does this read the high-byte of the address or the value > of the address one page below the actual read (it is read before the > overflow carry is added to the high byte of the address)? $D700-D7FF is another free space. Without unplugging anything, I typed: A1300 LDY #$FF LDA $D720,Y BRK GF1300 The result: Acc. is left with $FD. (And the color in color RAM was all $D.) Got the same result when I typed it again.
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