Read documentation for the IO Pi HAT and need to make miner change to the Wabbit feedback wiring. The IO Pi pins as inputs have pull-up resistors. The Wabbit status output needs to provide a ground to pull the IO Pi down, NOT as originally conceived as a positive on active.
An update to HelpNDoc is available IF my internet had not been down all week!
The Wabbit/IO Pi interface doesn't work. The IO Pi includes a 100K Ωpull up resistor. At 5v0dc that is only 0.05 ma (milli amps). I don't think that is enough current to push through the optic isolators. Testing shows that turning off the internal pull up and using a 22K Ω resistor results in 0.27 ma and it works! Value is open for change based on what resistor values are available in an IC array.
Without the internet, cleaning up some documentation.