User Port on Micro / Master

[simmerz]

Is there any means of emulating the User Port? Here's my use case:

I've recently been reunited with a Lego Technic programmable systems pack I had as a kid and wondered if I really needed to also retrieve my Master 128 or if I could use a Pi to drive it.

I'm wondering if the GPIO pins on a Pi could be used somehow to build a User Port, and then if b-em could use that to drive the Lego kit (and other stuff).