Stuff pertaining to implementing Posibus peripherals.
<UL>
<LI><b>io</b> is a template with the board outline and stacking headers.</LI>
<LI><b>PPaddle</b> is the basic Posibus paddle card, for making cables.</LI>
<LI><b>NPaddle</b> is the Negibus paddle card, for making cables.</LI>
<LI><b>MMU8L</b> is a compatible MMU for the PDP-8/L.</LI>