FX Series Programmable Controllers STL Programming 3
3-2
3.2 How STL Operates
As previousl
mentioned, STL is a s
stem which
allows the user to write a pro
ram which functions
in much the same wa
as a flow chart, this can be
seen in the dia
ram opposite.
STL derives its stren
th b
or
anizin
a lar
er
pro
ram into smaller more mana
eable parts.
Each of these parts can be referred to as either a
state or a step. To help identif
the states, each is
iven a unique identification number. These
numbers are taken from the state rela
devices
(see pa
e 4-6 for more details).
3.2.1 Each step is a program
Each state is completel
isolated from all other states within the whole pro
ram. A
ood wa
to
envisa
e this, is that each state is a separate pro
ram and the user puts each of those
pro
rams to
ether in the order that the
require to perform their task. Immediatel
this means
that states can be reused man
times and in different orders. This saves on pro
rammin
time
AND cuts down on the number of pro
rammin
errors encountered.
A Look Inside an STL
On initial inspection the STL pro
ram looks as if it is a rather basic flow dia
ram. But to find out
what is reall
happenin
the STL state needs to be put ‘under a microscope’ so to speak.
When a sin
le state is examined in more detail, the sub-pro
ram can be viewed.
With the exception of the STL instruction, it will be
immediatel
seen that the STL sub-pro
ram looks
ust like ordinar
pro
rammin
.
The STL instruction is shown as a ‘fat’ normall
open contact.
All pro
rammin
after an STL instruction is onl
active when the associated state coil is active.
The transition condition is also written usin
standard pro
rammin
.
This idea re-enforces the concept that STL is reall
a method of sequencin
a series of events or as
mentioned earlier ‘of
oinin
lots of smaller
pro
rams to
ether’.
M8002
X0
X1
S 0
S 26
X0
X1
X15
S 22
S 27
T0
T7
S 22
T0
1
2
STL
S 22
SET S 27
T0
Y22
K20
2
1
T0
