[Coco] Upgrade MPI?

[Sean]

Well, I don't know what to say to that, because upgrading the PAL chip
fixed my problems.
Note this wasn't an official RS-232 PAK, but a DC Modem Pak converted to an
RS-232 Pak.  My terminal software was Ultimatern.

On Thu, May 7, 2015 at 9:18 AM, Gene Heskett <gheskett at wdtv.com> wrote:

> On Thursday 07 May 2015 09:34:57 Sean wrote:
> > One issue I had with a non-upgraded MPI back in the day was that I
> > couldn't use any terminal programs with an RS-232 pak, characters
> > would get dropped and garbled with my blazing fast 2400 baud modem.
>
> That is an entirely different fix.  You need to bridge all 4 sockets
> together at each's pin 8, then remove 3 of the 4 pullup resistors which
> are now in parallel and causing some video flicker because of the excess
> current being used to report the IRQ. In this manner you are bypassing
> the IRQ selection logic in the mpi, so IRQ's from the rs232 pack are not
> blocked therefore causing that error.  The drivers are more than smart
> enough to locate and service the IRQ without the useless blocking.
>
> This is totally unrelated to the coco3 vs gime problem.  That is because
> of the insufficient decodeing of the address lines in the mpi when
> software tries to write to $FF7F to change slots, OR when os9 writes to
> the mmu registers in the gime at $FF9F, that write is ghosted to $FF7F,
> changing both the slot and the IRQ path, so they muck with each other.
> The MPI fix that stops that ghosted writing is a different fix.
>
> Keeping that straight in peoples minds is, I find, a bit like herding
> cats. ;-)
> >
> >
> > On Thu, May 7, 2015 at 8:16 AM, Christopher Barnett Fox
> > <cbfox01 at syr.edu>
> >
> > wrote:
> > > What are the "symptoms" of a non-upgraded MPI? I have one connected
> > > to my CoCo 3 today, and everything seems to work fine. Is there a
> > > specific operation we could perform that would demonstrate the
> > > issue?
> > >
> > > I recall someone on the list was working on a modern MPI
> > > replacement. Is that project at the point where a kit or finished
> > > product is available to purchase?
> > >
> > > Thanks!
> > >
> > > christopher
> > >
> > > On 2015/05/06/, 6:23 PM, "Robert Gault" <robert.gault at att.net> wrote:
> > > >Joe Grubbs wrote:
> > > >> Through sheer blind luck I have acquired a Tandy branded 26-3124
> > > >> MPI. It looks barely used, and more importantly, the OE warranty
> > > >> sticker is still in tact. Because it is "virgin" I'm reluctant to
> > > >> give it the CoCo3 PAL upgrade. Am I being ridiculous?
> > > >
> > > >If you want to use it with a Coco3, upgrade it! It really is not an
> > > >"upgrade to
> > > >make it 'better'" but a required change to prevent ghosting of I/O
> > > > bytes into
> > > >the GIME region. If you intend to use it with a Coco1 or 2, you do
> > > > not need to
> > > >make any changes.
> > > >
> > > >
> > > >--
> > > >Coco mailing list
> > > >Coco at maltedmedia.com
> > > >https://pairlist5.pair.net/mailman/listinfo/coco
> > >
> > > --
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> > > Coco at maltedmedia.com
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>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
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