1. Instruction description
Step Control (STL) is controlled by several operating procedures (S0,S1……Sn).
Step Control method’s feature is that after taken into considerations for each control step and divided the complex procedure into successive steps, it greatly reduces the interdependence between each step and the complexity involved in programming.
Every movement executed in each status are programmed by other instructions in the ladder diagram. STL is the initiation instruction for step procedures, and RET is the ending instruction for a step procedure.
After the instruction is executed, it returns to the bus bar.
SET S[k]([k] is in decimal) is the only instruction for initiating STL transitions. Note: STL—RET instructions cannot be used in sub-programs.
When transition is happening from current status (S0) to next status (S1), the actions under the two scanning cycle conditions will both be executed; when the next scanning cycle is being executed, current status (S0) will be reset by the next status (S1), and the actions under the current status (S0) will not be executed. All OUT components’ inputs will be interrupted.
Generally speaking, RET will be omitted between each step procedures. Therefore, it will seem a RET is shared by several STL. When STL is programmed and RET procedure is not, error message will appear.