Re: A89: Re: Re: Re: Re: CORRECTION: Shift+ON


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Re: A89: Re: Re: Re: Re: CORRECTION: Shift+ON




On Sat, Aug 19, 2000 at 02:06:36PM +0200, Jean Canazzi wrote:
> 
> Well, 256k is only 18 bits, so what does it have to do with the 24 bits
> address bus of the 68000 ? For me, the fact that the 68000 only have a
> 24 bits address bus just means that the higher byte will always be
> ignored (btw, isn't this property used somewhere in TIGccLib ?).

The RAM address range is only partially decoded and the RAM is repeated over
and over again to fill the entire 2MB at $000000-$1FFFFF. However, the
security chip lives in the range $040000-$1FFFFF.

TIGCCLIB uses the fact that the upper 8 bits [of PC] are ignored in
addressing. (I don't know why/when though. :) )


/Johan



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