On 10 Aug 2012 at 19:21, Fred Jan Kraan wrote: Tristate pins are easy--just add a controllable low current source to your rig for each prospective output pin. Try to "push" the subject pin one way or the other. If it's tristated, there is some combination of inputs that will cause it to assert a logic state and it will not be possible to "nudge" it--then you have not only the knowledge that it's a tristate, but what combination of inputs cause it to go active. You could implement this as a single pin driving several diode- isolated resistors. That worked for me. Registers and internal feedback remains an unsolved issue, however. --Chuck