Going back to your Post 10 and Fred's Post 4, is seems that your goal is simply to shut down the processor.

Before you invest any more time in this project, simply pull the power cord from the processor when you want it to shut down. Then restore power when you want the processor to restart. Does the system still behave normally? Potential issues could be that the processor will not restart after simply restoring power or that the processor will drop some settings or will require an unreasonable amount of time to resume operation.

If the processor behaves well enough under these conditions, then use a trigger output and relay to control power to the processor.