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

[KnudsenMJ at aol.com]

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.