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| From: Bionic (all posts)
Date: 2000-08-07
Subject: Re: Plus 4 Database Update
|
> > > Not quite, but a similar level of complexity. Do you have details of this
> >
> > uhm well.. swap one ls257 for a ls153 :)
>
> I'll explain my expansion's principle; an 8 bit latch, two four-to-one
> multiplexors and address decoding logic to map the latch to $FD7x. The
Hannes extension managed this by (ab)using the CS signal for the userport
6529. He used a LS138 to map more than one 6529 into the userport I/O space. ($FD10-$FD1F ?)
> latch could be a 6529 for read / write capability, but as these are rare I
> specified a 74 series part which would be write only. The 8 bits are
> divided into four groups of 2 bits; for each of the combinations 00, 01,
> 10 and 11 of A15 and A14, the hardware generates A17 and A16 which allows
> four different banks selectable in each 16K block. I like to think it's
> quite versatile, however, the main reason for the design is its
> simplicity, so if there is something simpler it will have effectively been
> obsoleted.
Well - Hannes extension is not that versatile. But people used it anyways.
There is an enhanced version of this extension by CSORY and Chr. Schäffner,
which allows more versatily page mapping. (all 16 block mappable into a single 16k block)
> > > very simple Hannes expansion? I don't think I've ever seen a diagram of a
> > > circuit that simple. The ones I have seen have been far more complex.
> >
> > The basic extension maps bank 3 to $0000-$1000 or to $0000-$4000
(choosable
> > with one bit) and bank 0-3 into the space above this. Thats it.
> > There is another slight extension to redirect all TED DMAs to bank 3
when
> > a bit is set.
>
> Please, can you send me or point me to fuller details of this expansion,
> such as circuit diagrams?
I have the schematics on paper at my parents home, so I dont have access right now. Its really quite straighforward.
I recommend you to ask Christian Schäffner for them. His homepage is at surf.to/solder
> > > The reason I developed this alternative expansion is that I was already
> > > developing one for the C64 and C128 and it uses the same principle, so I
> > > can re-use the hardware between the machines. If it really is as simple as
> > > the simplest Hannes expansion then I will of course abandon development
> > > and build a Hannes 256K plus/4 instead.
> >
> > Probably the better choice. Getting software support for a new plus/4
> > 256kb extension is nowadays a bit difficult :)
>
> I would patch older programs myself, of course, and even then I'd only get
> time to do the ones I'm interested in. I understand there's a large amount
> of 256K-supporting plus/4 software, so perhaps I've underestimated the
> enormity of this task. However, I've never encountered much on my
> searches.
How about using a GAL for the page decoding ? :) So you could make a switchable extension.
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