Re: 74ls612, clocking 6502and others...
Date: 1998-04-23 20:21:25

Hallo Andre,

> This seems reasonable. Open inputs normally read as high anyway (due to
> internal pullups)

Then explain me the $DE00/$DFFF trick of Marko :-) In this case the databus 
reflects something originated by the VIC. But there is an old saying here in 
the Netherlands: "Baadt het niet, schaadt het niet" (If it does not help, it 
does not hurt either).

> Hae? changing the mapping in the middle of the write will cause a 
> 'half-write' (or what you like to call it) to the newly mapped address?
> I don't think I get the point. 

The only thing I do is disabling the mapping. This means that the output does 
NOT reflect one of the registers. So I safely can change them. 

> Hm. You should probably think of mapping the addresses $000000-$0fffff 
> (1MByte)
> with the MMU, i.e. with slow access. Then you can have some additional 
> RAM in this space to replace the ROMs for example, which you couldn't do
> otherwise (without sacrificing 8032 RAM for this purpose).

I think you missed the point. A16-A23 of the CPU and those of the MMU are 
placed PARALLEL! Which lines are active depends if the 65816 is in the area 
$000000/$00FFFF or not. This means I can replace ROM with RAM form every other 
big page I want.

> See out Phi2 discussion. I would rather use bus driver to decouple the
> busses. You should at least mention that, I think.

Thanks, forgot to correct this one.

Groetjes, Ruud

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