Re: Hardware emulation of 6509 using 6502?

From: Mia Magnusson <mia_at_plea.se>
Date: Sat, 28 Jul 2018 12:25:46 +0200
Message-ID: <20180728122546.0000375f@plea.se>
Den Fri, 27 Jul 2018 09:37:19 +0100 skrev smf <smf@null.net>:
> On 27/07/2018 04:03, Mia Magnusson wrote:
> > ... and then someone moves chargen v.s. video ram around and the
> > emulation can't really know which pokes were supposed to go to a
> > pre buffered screen ram v.s. chargen.
> 
> I believe the VIC20 can only have video ram & chargen in 4k of the 
> internal ram.

5k. But yes, from basic you could practially only use the cassette
buffert and some other parts of the ram under address 1024.
 
> You should be able to store both representations of video ram and 
> chargen in a 16k VIC2 bank.
> 
> The problem is finding any software that makes it worthwhile.

I don't know how common it is, but a trick to be able to use both
custom characters and the built in charrom is to set the chargen
pointer so half of the charset is in ram and half is in rom. That way
you end up having 1k with the non-inverted rom font (upper case +
graphics) mapped at char 128-255, and custom chars in the upper 1k of
the built in ram mapped at char 0-127. If you want to use more than
about half of those chars, you need to move the screen ram. And if you
move screen ram after having done any pokes, the emulator won't always
know what to do with some of the data you have poked.

Today there is of course no reason to emulate a VIC 20 on a C64, you
can either get a real VIC 20 or emulate on a modern computer.


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Received on 2018-07-28 13:00:04

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