I came across this thread answer from crutschow and wanting to know the easy way to control this circuit from one signal coming from the MCU (inverter, flipflop, more transistors arranged in a certain way?). The load isn't that much for my application because I'm only wanting to control the voltage of a pullup resistor.
Attached is a block diagram of the circuit I would like to finish building:

No relays!!

 

Probably there will be a problem because of the internal reverse diode in some FET devices. Also, the whole issue does not make any sense. Si a more detailed explanation is a good idea, so we can understand.

 

Probably there will be a problem because of the internal reverse diode in some FET devices. Also, the whole issue does not make any sense. Si a more detailed explanation is a good idea, so we can understand.

I basically want a configurable pullup resistor that can be pulled up to two different power rails. I would like to it to switched from one GPIO