[Coco] Re: [Color Computer] mystery chip on COCO2 XC80652P

[jdaggett at gate.net]

Mike 

Since the MC6822 is Depletion load NMOS technology, it is correct 
to call it open drain over open collector but essentially just different 
transistor geomotry.

Correct the source current is limited by the pullup resitor and the 
sink current is limited by the chanel width of the MOS ouput 
transistor, which is about 1 TTL level or about 2 ma. 

The MOS capabilities is 18 V. Thus the highest voltage that one can 
pull the output MOS device up to is 18 VDC. 


Now open plate, or thermionic valves. I brought a nice 500 watt 
plate dissipation tube into work one day and some of the young 
engineers were amazed. Yep tube theory is not taught anymore in 
engineering at colleges. Most engineers coming out of college 
would hardly know what ot do with a vaccum tube. Some duds 
make great lamps though. Take the 3-500Z tube requires 45 watts 
for jsut the filaments. 

I always liked a linear amps for amatuer radio that used mercury 
vapor rectifiers. As you spoke you can see the purple glow of the 
rectifiers glow stronger on voice peaks. One could almost tune the 
amp just by watching the rectifier tubes. 

james

On 7 Mar 2004 at 22:22, KnudsenMJ at aol.com wrote:

From:           	KnudsenMJ at aol.com
Date sent:      	Sun, 7 Mar 2004 22:22:16 EST
Subject:        	Re: [Coco] Re: [Color Computer] mystery 
chip on COCO2 XC80652P
To:             	coco at maltedmedia.com
Send reply to:  	CoCoList for Color Computer Enthusiasts 
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> In a message dated 3/7/04 9:35:29 AM Eastern Standard Time,
> jdaggett at gate.net writes:
> 
> > Neither port is open collector.
> >  
> >  Both Port A and Port B are open Drain.
> 
> Same thing logically, except for the reduced current rating.  Just
> different terms for CMS and bipolar TTL.  (When I learned electronics,
> it would have been "open plate", so there :-)
> 
> > Maximum pullup voltage is 
> >  18 VDC. Each port pin must have an external pullup resistor. Not
> >  sure but the sink and source currents are not very high. Maybe one
> >  TTL level ~2 ma.
> 
> Being open-whatever, there is no source current available.  Except
> what your pullup resistor lets thru when the output is HIGH.
> 
> Hope this reduces, rather than adds to, the confusion -- Mike K.
> 
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