FX Series Programmable Controllers STL Programming 3
3-11
3.7 Using STL To Select The Most
Appropriate Program
So far STL has been considered as a simple flow chartin
pro
rammin
lan
ua
e. One of
STL’s exceptional features is the abilit
to create pro
rams which can have several operatin
modes. For example certain machines require a selection of ‘manual’ and ‘automatic’ modes,
other machines ma
need the abilit
to select the operation or manufacturin
processes
required to produce products ‘A’, ‘B’, ‘C’, or ‘D’. STL achieves this b
allowin
multiple pro
ram
branches to ori
inate from one STL state. Each branch is then pro
rammed as an individual
operatin
mode, and because each operatin
mode should act individuall
, i.e. there should be
no other modes active; the selection of the pro
ram branch must be mutuall
exclusive. This
t
pe of pro
ram construction is called “Selective Branch Pro
rammin
”. An example
instruction pro
ram can be seen below, (this is the sub-pro
ram for STL state S20 onl
) notice
how each branch is SET b
a different contact.
A pro
rammin
construction to split the pro
ram flow between different branches is ver
useful
but it would be more useful if it could be used with a method to re
oin a set of individual
branches.
This t
pe of STL pro
ram construction is called a “First State Mer
e” simpl
because the first
state (in the example S29, S39 or S49) to complete its operation will cause the mer
in
state
(S50) to be activated. It should be noticed how each of the final STL states on the different
pro
ram branches call the same “
oinin
” STL state.
Y0
X0
X1 X2
S
Y
X
S
X
S
X
S
20
0
21
1
31
2
41
STL
OUT
LD
SET
LD
SET
SET
LD
0
S 21 S 31 S 41
S 20
Y10
S 29
X10
S 39 S 49
X11 X12
Y11
Y12
S 50
STL
OUT
S
Y
39
11
STL
OUT
S
Y
49
12
LD
SET
X
S
10
50
LD
SET
X
S
11
50
LD
SET
X
S
12
50
STL
OUT
S
Y
29
10
