Sequential　circuit　is　a　common　logic　device　whose　output　values,　at　a　given　instant,　depend　upon　its　input　values　and　the　internal　state　at　that　instant,　and　whose　internal　state　depends　upon　the(66)preceding　input　values　and　the　preceding　internal　state.　A　sequential　circuit　can　assume　a　finite　number　of　internal　states　and　may　therefore　be　regarded,　from　an　abstract(67),　as　a　finite(68).Combinational　circuit　is　another　logic　device　whose　output　values,　at　any　given　instant,　depend　upon　the　input　values　at　that　instant.　A　combinational　circuit　is　a(69)of　a　sequential　circuit　whose　internal　state　is　not　taken(70).