Re: SuperCPU for my C64 and C128

From: Mia Magnusson <>
Date: Tue, 24 Jul 2018 00:48:19 +0200
Message-ID: <>
Den Mon, 23 Jul 2018 22:54:26 +0100 skrev smf <>:
> On 23/07/2018 21:34, Mia Magnusson wrote:
> >> If you add an ultimax mode then you still have to mirror ram at the
> >> start of memory, but you have to solve the problem of interleaving
> >> the 1mhz vic reads into the 20mhz cpu reads.
> > The speed of the VIC-II reads won't be a problem, it's just a
> > matter of inserting one wait state for the 65816
> You'll be doing bidirectional memory accesses across a bus where both 
> sides run off different clocks.

No, the VIC can only read, never write, so it's unidirectional. And I'm
assuming buses in sync.
> I'm not saying it can't be done, but you have to do it & there will
> be headaches

1 or even 2MHz is slow compared to for example 20MHz. With a 20MHz
"memory clock" you have 5 memory clock cycles for each VIC read cycle,
that gives you plenty of time to insert a wait state, do the actual
read and latch the data for VIC to read whenever the 1MHz cycle is in
the state where VIC reads the data.

> >> You still need to support all the supercpu mirroring schemes as
> >> well, or you won't be able to get the correct timing for demo
> >> effects.
> > Will 6510 based demos work at all on a 65816? I'd assume that they
> > use some well known illegal op codes?
> You misunderstood, I am talking about 65816 demo effects.

Oh. I didn't even know that there are such things. :)

> I don't know how many 6510 demos use illegal opcodes, but none of my
> old demos used them though.

Some of the illegal op codes kind of begs to be used though. I
understand that few used them back in the days as noone knew if there
would be a C64-II that didn't implement them, and there were no easy
way to check if they do work on many different C64's. But nowdays there
won't be any new C64 without them and it's well known that they exist
in every C6t4.

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Received on 2018-07-24 01:00:18

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