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