module CombLock
Title 'Combination-Lock State Machine'

" Input and Outputs
X, CLOCK       pin;
UNLK, HINT     pin istype 'com';
Q1, Q2, Q3     pin istype 'reg';

Q = [Q1..Q3];

Equations

Q.CLK = CLOCK; " Q.OE = 1;

" State variables
Q1 := Q1 & !Q2 & X  #  !Q1 & Q2 & Q3 & !X  #  Q1 & Q2 & !Q3;
Q2 := !Q2 & Q3 & X  #  Q2 & !Q3 & X;
Q3 := Q1 & !Q2 & !Q3  #  Q1 & Q3 & !X  #  !Q2 & !X
      #  !Q1 & !Q3 & !X  #  Q2 & !Q3 & X;

" Mealy outputs
UNLK = Q1 & Q2 & Q3 & !X;
HINT = !Q1 & !Q2 & !Q3 & !X  #  Q1 & !Q2 & X  #  !Q2 & Q3 & X
       #  Q2 & Q3 & !X  #  Q2 & !Q3 & X;    

end CombLock