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

Tue May 8 09:30:40 EDT 2007

james,

Trying not to laugh....(count the # of times you used the term TTL..... :)

You are talking general about LS and common knowledge about logic  
families. I was talking specifically about the LS245 and the CoCo.

Mark
Cloud-9

Quoting jdaggett at gate.net:

> 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
>> >> >>>>>
>> >> >>>>> --
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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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>> >
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>>
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