求各位老師指點

在使用STL步進指令時,在之前必須加個狀態轉換條件.X,T,或M.如
---II-----[SET S0]
M8000
---ISTL S0I-----II-------[SET S20]
                          S0
---ISTL S20I---------------(YO)
                         -------------(T0 K10)
                           T0
                         ---II---------[SET S21]
----ISTL S21I---------(Y1)
                          ----------(T1 K10)
                               T1
                          ----II-------(S0)
                          ---------------[RET]
先寫狀態轉移圖,再編寫...
2樓的同志錯了..RET是步進返回指令.....SRET才是子程序返回指令..