Below is a sequential circuit and the skeleton of a state diagram.  You will reverse engineer the circuit to re-derive the state diagram by following the steps and answering the questions below.

Is the circuit above a Mealy or Moore machine?

Mealy (output is function of input and current state)

What are the next state equations (for D1, D2, D3) and the output (Z)?
 

   D1 = X'Q3 + XQ2

   D2 = XQ3 + X'Q1

   D3 = X'Q2 + XQ1

   Z = XQ1 + XQ2
 

Start at state 001 (Q1 = 0, Q2 = 0, Q3 = 1) and complete the state diagram below.  Show all state transitions from state 001 (for both X = 0 and X =1) and for each state reachable from 001.  Please put all the X = 1 transitions on the top and all the X = 0 transitions on the bottom.
 

Are there any unreachable states?  If so, which?  Assume that 001 is that start state.

Yes, 000, 011, 101, 110, and 111 are all unreachable states if the machine starts in state 001.

Is this a self-starting machine?  Why or why not?

The complete state diagram is shown below.

No, it is not self-starting because if the machine starts in state 000 is will remain there (similarly for state 111).  Furthermore, the machine will also be trapped in the three state set: 011, 101, and 110 if it starts in any of those states.