6.18.1 STL, RET instructions

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.

Program example

Example 1

In example 1, 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.

Example 2

State transfer could only use the SET instruction, couldnot use OUT instructions.

Example 3

Time relay T could be reused, but the adjacent two states couldnot be reused using the same time relay.

Note for use

• STL---RET instructions couldnot be used in sub-programs.
• When transition is happening from current status (S0) to next status (S1), the actions under the two scouldning cycle conditions will both be executed; when the next scouldning 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.