Finally got my clock circuit up and running. I'm using a wire for the break signal to check it out. When the break is enabled, it overrides the Select button and selects the Step function. Pushing the step button will then step past the break instruction and then return control back to the oscillator. I'm still not totally happy with how it handles the transition between clock domains, so I may end up pulling all this out and starting over. But not yet - I have way too much else to do.