[Coco] rcrislip at neo.rr.com

[Gene Heskett]

On Saturday, February 07, 2015 10:12:14 AM Chad H wrote:
> The whole "PIA" keeps getting me.  Since I don't know what it really
> means my brain keeps reverting to "pain in a$$"

PIA=Peripheral Interface Adaptor=a 6821 or 6822, one has open collector 
outputs meaning it can only pull down to about .1 volts, the other is a 
normal TTL "totem-pole" output, a quick and dirty push-pull output, with the 
sink side transistor being the strong one. 

They can pull up, but runs out of pull at about 3.5 volts UNLESS there is a 
cmos version, which I am not aware of, but which could in that event pull 
rail to rail in its output voltage swing ability.  There are CMOS versions 
made I'm sure, but the likelood of being a footprint dropin replacement is 
probably pretty low,

While I am on a roll at this, CMOS=Complimentary Metal Oxide Semiconductor.

Easily destroyed by its inputs being subjected to static discharges. A 
single  electron forced thru the gate insulating silicon dioxide layer 
wrecks it)  In a steady state condition it draws only the power being 
delivered to its outputs.  The only other power it uses is that needed to 
charge and discharge the gate capacitance because it is effectively a large 
capacitance from the atomic layer thickness between the plates of the 
capacitor that forms the transistors structure.

Speed limited in the original 4000 family of chips from RCA by how fast it 
can charge or discharge the gate of the transistor, rated at a max of 15 
volts for its logic supply, but in reality tough as nails. I once used the  
4000 stuff in a very very early  character generator made by 3M in about 
1977, adding a color controlled border around the characters. But as that 
took sub-microsecond speeds to do that, I used both the + and minus supplies 
available, which totalled up to 28 volts, but only on the edge decoder, a 
4028.  It ran with detectable heat doing that but did it for quite a few 
years without a failure.

The technology has advanced enough today that it can now run at gigahertz 
speeds for the newer chips.

I'll get me coat now.  :)

[...]

Cheers, Gene Heskett
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