On Fri, 19 Mar 1999, Patrick Kramer wrote:
> > > This mystery can be solved quite simply if you look at the
> > specifications of
> > > the MSX slot. In a cartridge slot, you have three signals, just for the
> > > convenience of the hardware designer:
> > > CS1: This signal becomes active if the Z80 addresses memory in page 1
> > > CS2: This signal becomes active if the Z80 addresses memory in page 2
> > > CS12: This signal becomes active if the Z80 addresses memory in page 1
> > or 2
> >
> > I already knew this signals, but I never understood how to create a ROM in
> > pages 0 and 3.
> Well, you don't need these signals then.
> Example: if you want to have a 16K ROM in page 0, you would have to
> select this ROM whenever the slot is selected, AND address space 0000-3fff
> is addressed. This means A14 and A15 MUST be low.
> So as a _CS for the ROM you would have _SLTSL OR A14 OR A15.
Wow! Now many many things are becoming clear!!!
> > But how can be made cartridges with 64kb of normal continuous RAM?
> >
> Well, only use _SLTSL as a _CS for the RAM. There is no need for
> page-related chip selects as all pages are addressed.
> (A14 and A15 are used)
That's what I was thinking. I don't know why here, in Brazil, we had had
many informations about software, but almost nothing about hardware.
Greetings from Brazil!
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Marco Antonio Simon Dal Poz http://www.lsi.usp.br/~mdalpoz
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