FX Series Programmable Controllers STL Programming 3
3-5
3.4 Moving Between STL Steps
To activate an STL step the user must first drive the state coil. Settin
the coil has alread
been identified as a wa
to start an STL pro
ram, i.e. drive an initial state. It was also noted
that usin
an OUT statement to drivin
a state coil has a different meanin
to the SET
instruction. These difference will now be explained:
3.4.1 Using SET to drive an STL coil
• SET is used to drive an STL state coil to make the step active. Once the current STL step
activates a second followin
step, the source STL coil is reset. Hence, althou
h SET is
used to activate a state the resettin
is automatic.
However, if an STL state is driven b
a
series of standard ladder lo
ic instructions,
i.e. not a precedin
STL state, then
standard pro
rammin
rules appl
.
In the example shown opposite S20 is not
reset even after S30 or S21 have been
driven. In addition, if S20 is turned OFF,
S30 will also stop operatin
. This is
because S20 has not been used as an STL
state. The first instruction involvin
the
status of S20 is a standard LoaD instruction and NOT an STL instruction.
• SET is used to drive an immediatel
followin
STL step which t
picall
will have a lar
er
STL state number than the current step.
• SET is used to drive STL states which occur within the enclosed STL pro
ram flow, i.e.
SET is not used to activate a state which appears in an unconnected, second STL flow
dia
ram.
X000
SET S021
S040
S020
RST S022
S020
S030
Note:
If a user wishes to forcibl
reset an
STL step, usin
the RST or ZRST (FNC
40) instructions would perform this task.
