[Coco] Grr!!! Bad MPI! No biscuit!

Mon May 7 22:55:53 EDT 2007

On 7 May 2007 at 9:02, Mark Marlette wrote:

> Robert,
> 
> The LS245 has hystersis which helps in the noise arena. F245 doesn't.
> 
> I wouldn't switch them.
> 
> Regards,
> 
> Mark
> 
*************

Noise immunity becomes a major issue only when you are mixing different 
classes of TTL logic. LIke LSTTL and STTL or LSTTL and FTTL. LSTTL to 
CMOS. When looking at low level state margins there is no difference between 
LSTTL and FTTL family for commercial grade. With High Level logic state FTTL 
has better noise immunity than LSTTL when you at greater extents from typical 
VCC voltages. 

Even with hysteresis, I would prefer FTTL over LSTTL for noise immunity. In fact 
I would take TTL over LSTTL. LSTTL inherently has noise issues. In order to 
reduce power draw that input circuitry to the gates have been redesigned. What 
this does is improves power efficiencies at lower speed switching and at steady 
state. FTTL is nothing more that a speed increase of the old standby TTL logic. In 
order to gain speed advantages FTTL have higher steady state currents. They 
also have larger overall geometry for the transistors and thus more current source 
and sink capabilities. FTTL have better power efficiency at higher clock rates than 
do LSTTL. 

james

> Quoting coco at yourdvd.net:
> 
> > I believe Marty Goodman once recommended that the ls245 in the CoCo
> > AND the MPI be replaced with a faster version (the ''F'' version, I
> > think he mentioned). -r
> >
> >> -------- Original Message --------
> >> Subject: Re: [Coco] Grr!!!  Bad MPI!  No biscuit!
> >> From: Gene Heskett <gene.heskett at verizon.net>
> >> Date: Sat, May 05, 2007 1:48 pm
> >> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> >>
> >> On Saturday 05 May 2007, Joel Ewy wrote:
> >> >Gene Heskett wrote:
> >> >> On Saturday 05 May 2007, Joel Ewy wrote:
> >> >>> Jim Cox wrote:
> >> >>>> I have a MPI board that someone gave me.  I am not sure if it
> >> works or
> >> >>>> not, but it's yours.
> >> >>>>
> >> >>>> Jim
> >> >>>> PS: We need a new MPI for the CoCo
> >> >>>
> >> >>> Here's a humble suggestion for anyone contemplating such a
> >> >>> thing: Orient the board perpendicular to the desktop so that
> >> >>> any cartridges plugged into it will be parallel with the
> >> >>> desktop.  Having the disk controller stick up 8.5" from the
> >> >>> surface of the desk is just a bit silly.
> >> >>>
> >> >>> As much as I loathe trying to find places to plug them all in,
> >> maybe an
> >> >>> external transformer would be a good idea here...
> >> >>>
> >> >>> Would it be feasible to put bi-directional bus drivers in a
> >> >>> short cartridge and connect the CoCo to the MPI via a short
> >> >>> length of
> >> ribbon
> >> >>> cable?  That would provide much greater flexibility in
> >> >>> placement, and probably reduce the chances of bumping things
> >> >>> out of place.
> >> >>>
> >> >>> JCE
> >> >>
> >> >> This idea falls over due to a bus contention in the mpi's
> >> >> internal
> >> timing,
> >> >> which in turn causes a ground bounce that is only barely
> >> >> tolerable
> >> if the
> >> >> grounding ear clips in the side port have a good clean grip on
> >> >> the
> >> mpi's
> >> >> ground plane.  Additional jumpers of heavy wire to tie the mpi's
> >> rather
> >> >> surpentine ground plane together also help, as does additional
> >> bypassing
> >> >> near the ls245.  You can make it stable, as shipped, its a house
> >> >> of
> >> cards.
> >> >
> >> >Are you saying that this problem is intrinsic to any CoCo
> >> >multi-pak design, or just Rad Shak's?  FWIW, I'm musing about a
> >> >possible future product, not modifications to the existing design.
> >>
> >> I'd say it would be pretty well builtin, Joel, unless someone
> >> actually went to the trouble of fixing the timing problems, which
> >> are in actual fact quite narrow, existing for not more than 10ns,
> >> but during that time its an absolute crowbar across the ls245 in
> >> the mpi, and whatever is driving the buss on the coco's side of the
> >> edge connector.  The ground bounce, measured from the coco's ground
> >> plane, say at the contact ears, over to a ground plane connection
> >> around the ls245 and its environs, can exceed a volt for 8 to 10 ns
> >> in the shacks first version.  The mods I made to mine pull it down
> >> to around 150mv, but its still there.  They also lowered the
> >> operating temperature of that ls245 by a noticeable with the back
> >> of your finger amount.
> >>
> >> I think, but won't swear, that its the turn around delay in the
> >> ls245 itself, and that one of the faster chip families version of
> >> it might alleviate it at least as well as the extra grounds and
> >> bypassing I added to mine did.  I should have taken the time to
> >> socket it and experiment but didn't. :(
> >>
> >> There needs to be a few ns of dead time, where the ls245 is truly
> >> open in both directions on a switch in directions, but I'm not sure
> >> how one would go about separating the read and write functions in
> >> order to achieve a buss that's tri-stated on both sides of it. 
> >> That is whats needed to eliminate it though. I'd guess that 5ns of
> >> dead time would be sufficient, based on what my measly 100mhz dual
> >> trace scope says.  5ns is of course faster than my scope, but it is
> >> useable to around 200 mhz as I've used it to look at a channel 8 tv
> >> transmitter (175mhz), just not anywhere near full height traces
> >> when stuff that fast goes by. 10ns should cover it all, and that
> >> still leaves the coco with a couple of eons to do stable reads and
> >> writes through it.
> >>
> >> >JCE
> >> >
> >> >>>> On Sat, 5 May 2007 03:12:01 -0600
> >> >>>>
> >> >>>>  Willard Goosey <goosey at virgo.sdc.org> wrote:
> >> >>>>> My old-style MPI is apparently toast.  My CoCo has therefore
> >> >>>>> lost access to its hard drive.  :-(
> >> >>>>>
> >> >>>>> I suspect power supply problems.  Either that or the upgrade
> >> >>>>> PAL is loosing its mind.
> >> >>>>>
> >> >>>>> Just what I need, something else broken.
> >> >>>>> Willard
> >> >>>>> --
> >> >>>>> Willard Goosey  goosey at sdc.org
> >> >>>>> Socorro, New Mexico, USA
> >> >>>>> "I've never been to Contempt!  Isn't that somewhere in New
> >> >>>>> Mexico?"
> >> >>>>>   --- Yacko
> >> >>>>>
> >> >>>>> --
> >> >>>>> Coco mailing list
> >> >>>>> Coco at maltedmedia.com
> >> >>>>> http://five.pairlist.net/mailman/listinfo/coco
> >> >>>>
> >> >>>> --
> >> >>>> Coco mailing list
> >> >>>> Coco at maltedmedia.com
> >> >>>> http://five.pairlist.net/mailman/listinfo/coco
> >> >>>
> >> >>> --
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> >> >>> Coco at maltedmedia.com
> >> >>> http://five.pairlist.net/mailman/listinfo/coco
> >> >
> >> >--
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> >>
> >>
> >>
> >> --
> >> Cheers, Gene
> >> "There are four boxes to be used in defense of liberty:
> >>  soap, ballot, jury, and ammo. Please use in that order."
> >> -Ed Howdershelt (Author)
> >> Inara: "It wasn't entirely a disaster."
> >>
> >> Mal: "I got stabbed! Right here!"
> >>
> >> Inara: "You also lined up exciting new crime."
> >> 				--Episode #4, "Shindig"
> >>
> >> --
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> >> Coco at maltedmedia.com
> >> http://five.pairlist.net/mailman/listinfo/coco
> >
> >
> > --
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> >
> 
> 
> 
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