I have been wondering what to do on the BeefyDuino about the issue of selecting input or output mode, the use of the enable pins, and such. I have an answer.

Each SN743310 pair shares an enable pin, so connect the two in parallel to get one enable per output. Simple. This means each chip provides two outputs and we need six chips. Right.

Then, how to set the enable pin? Why, sniff the output of course! If the output is being driven high or low, then it is an output and enable should be high. if the output is hiZ or pullup, then it is an input and enable should be low. buffer the input so it is not driven by the input circuit and sense it with a window comparator. Oh, add an integrator to the comparator to make sure logic transitions don't throw it.

That way we get a super-muscled BeefyDuino with no change in pin functionality. It will take some design effort but I think the circuit is quite designable.

Les