Lee,

My experience is that most 805x devices use the conventional intel port hardware structure, called a quasi-bidirectional port. most of the digital ports can be used as either input or output.

also, at least on the phillips parts (8xc552 is my favorite), they ports are current limited. as long as you don't exceed 5.7 volts in to pin being used as an output, you can't overdrive them. they are current limited. once you hit 5.7 volts, the ESD protection diodes which go from the pin to V+ switch on and then you can damage the chip, at least the ESD diode part.

if you are using the pin as an output and it is high, then the current is limited to two distinct values. there is a fast pullup that is switched in for part of the low to hi transition to maximize the switching speed, then a weak pullup replaces it. it is only capable of sourcing a few hundred microamps. again, you are not going to damage the chip, even with a direct short to ground.

the neat thing about the -552 is that it has a 10-bit, 8 channel a2d in it anyway, rendering your example moot! (unless you need 12 or 16 bits, that is!).

good questions, though.


forrest