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5-24 Step Instructions
The step instructions STEP(08) and SNXT(09) are used in conjunction to set up
breakpoints between sections in a large program so that the sections can be
executed as units and reset upon completion. A section of program will usually
be defined to correspond to an actual process in the application. (Refer to the
application examples later in this section.) A step is like a normal programming
code, except that certain instructions (e.g., IL(02)/ILC(03), JMP(04)/JME(05))
may not be included.
5-24-1 STEP DEFINE and STEP START–STEP(08)/SNXT(09)
B: Control bit
IR, SR, AR, HR, LR
Ladder Symbols Definer Data Areas
STEP(08) B STEP(08)
B: Control bit
IR, SR, AR, HR, LR
SNXT(09) B
Limitations All control bits must be in the same word and must be consecutive.
IR 29800 to IR 29915 cannot be used for B.
Description STEP(08) uses a control bit in the IR or HR areas to define the beginning of a
section of the program called a step. STEP(08) does not require an execution
condition, i.e., its execution is controlled through the control bit. To start execu-
tion of the step, SNXT(09) is used with the same control bit as used for
STEP(08). If SNXT(09) is executed with an ON execution condition, the step
with the same control bit is executed. If the execution condition is OFF, the step is
not executed. The SNXT(09) instruction must be written into the program so that
it is executed before the program reaches the step it starts. It can be used at dif-
ferent locations before the step to control the step according to two different
execution conditions (see example 2, below). Any step in the program that has
not been started with SNXT(09) will not be executed.
Once SNXT(09) is used in the program, step execution will continue until
STEP(08) is executed without a control bit. STEP(08) without a control bit must
be preceded by SNXT(09) with a dummy control bit. The dummy control bit may
be any unused IR or HR bit. It cannot be a control bit used in a STEP(08).
Step Instructions Section 5-24