[Coco] Multi-Pak card edge connectors.

[Gene Heskett]

On Thursday 14 January 2010, jdaggett at gate.net wrote:
>On 14 Jan 2010 at 21:16, Gene Heskett wrote:
>> Also, using the S family of chips makes it very power hungry, and I don't
>> believe there is anything in this whole thing that cannot also be done
>> with the HCT chip family (<1% the power needed compared to S) unless that
>> particular function is not available in HCT, in which case I'd use the
>> next lowest power, probably the LS stuff.
>
>Gene
>
>I agree that there is no need for standard Schotky devices. Darn things are
> power hungry. HCT is the a better route. The Coco does not run that fast
> to require such devices. Also you can run into issues where an LS device
> driving one or more Schotky gates can run into fan out issues. Great care
> should be taken when mixing Schotky and LS devices so that you do not
> exceed the fan out of the LS devices.
>
>The input impedance for LS devices is in the order of 20K. Schotky devices
> are around 3K impedance. Also Schotky devices has a lower short circuit
> resister. Standard Schotky can source twice the current of an LS device.
>
>james
>
We should probably note too James,for the builders of these, or other such 
projects for that matter, that the HCT has essentially an infinite input 
impedance, and _any_ unused inputs _must_ be pulled high, although a resistor 
in the 100k-1meg range is sufficient.  That might require a pretty careful 
look at those schematics to find the 'unused' circuits.  Like where a 74xx00 
NAND gate is used for an inverter, but only has one input actually driven?  
Both inputs should be tied together in that case.  Every time.  Even for a 
plain old 7400.

People who design with TTL stuff who have forgotten that minor detail about 
unused inputs have caused some very exasperating field problems by what I can 
only believe is their stupidity.  One such highly intermittent case took me 
about 5 years to find, looking for it for half an hour here, and another half 
hour there, and it was built by Chyron, whom one would think would know 
better.  It was also returned to Chyron for repair, complaining about the 
intermittent, 3 times!  In all my years in the chasing electrons business, 
that was the second time I called the maker and asked to speak to the 
engineer whose name was signed off on the schematics, just so I could discuss 
his educational credits and genealogy with him in very pointed language.  
Those were pieces of my mind that were definitely both surplus, and a burr 
under my saddle that absolutely had to be removed by laying it on the person 
responsible.

Tonight?  I'm ready to call Antec, the computer psu maker.  The 3rd and last 
of 3 of them I've bought over the last 2 years died, didn't like the cold in 
the shop I guess.  Antec seems to be held in high regard, but to me, all they 
have managed to do is charge $90 for a supply I can get from any sidewalk 
vendor in Hong Kong for $6 US, and cut it to the quick internally so it dies 
not more than a month after the warranty expires.  No more of them will ever 
get a space rental here.

But, what good would it do?, so its a shrug, but I learned a lesson I don't 
mind passing on.  The Hi-Pro's I have seem to be well behaved, a 300 watter 
is running a quad core phenom on an ASUS mobo that's got something in every 
slot, and there are 4 HD's totaling 3.5 Tb to spin, and its as happy as a 
clam.

I'll go quietly, Officer. ;-)

-- 
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)

Robot, n.:
	University administrator.