Many of the bus signals are shared via open collector or open drain
outputs rather than via tri-stated signals; this is of course required for
some  asynchronous  things like the shared interrupt lines, and it works
well for other types of signals as well.  Of course, a backplane resistor
pulls these lines high, PICs only drive the line low.

        /own      /bgack     /cinh       /berr 
        /dtack    /reset     /int2       /int6 
        /hlt