> -----Original Message-----
> From: Marco Antonio Simon dal Poz [SMTP:[EMAIL PROTECTED]]
> Sent: vrijdag 19 maart 1999 13:12
> To: [EMAIL PROTECTED]
> Subject: Re: MegaRAM
>
> On Fri, 19 Mar 1999, Alex Wulms 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.
>
> > As you might understand, the cartridges which are 'mirrored' all over
> the
> > place simply ignore the CSx signals. While the megarom cartridges, which
> can
> > only be addressed in page 1 and 2, use the CS12 signal.
>
> Then, normal Konami Megaroms use CS12 signal, and Konami SCC Megaroms
> don't use. Is that right?
>
> > Funny to realize that all these amazing discoveries are well documented.
> We
> > should definetely get a good site up and running with all technical
> > documentation available about the MSX. It will save a lot of people a
> lot of
> > time with tracing and disassembling the MSX ROMS.
>
> Yes, it will save too much time!
>
> 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)
> Greetings from Brazil!
>
> -----------------------------------------------------------------
> Marco Antonio Simon Dal Poz http://www.lsi.usp.br/~mdalpoz
> [EMAIL PROTECTED] "Apple" (c) Copyright 1767, Sir Isaac Newton
>
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