> Or, to put it another way:  Whichever line goes low first is what the 
> bit is - a mark or a space.   The other processor acknowleges that it 
> saw the bit by yanking the opposite line low.  The sending processor 
> acknowedges that it saw the second processor got the bit by returning 
> it's bit to high, and the far end processor acknowleges this by turning 
> it's bit back high.
> 

Where have I seen this before -- Oh yeah, this is Texas Instrument's link 
protocol for thier calculators. I interfaced my TI-89 titanium to a 16F88 
a couple years back, one of my first projects with the '88 as I recall.

-Denny

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