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FX Series Programmable Controllers Devices in Detail 4
4-8
4.4.3 STL Step Relays
States (S) are ver
y
important devices when
pro
g
rammin
g
step b
y
step process control. The
y
are
used in combination with the basic instruction STL.
When all STL st
y
le pro
g
rammin
g
is used certain states
have a pre-defined operation. The step identified as
in the fi
g
ure opposite is called an ‘initial state’. All other
state steps are then used to build up the full STL
function plan. It should be remembered that even
thou
g
h remainin
g
state steps are used in an STL
format, the
y
still retain their
g
eneral or latched
operation status. The ran
g
e of available devices is as
specified in the information point of the previous
section.
Assigned states:
• When the applied instruction IST (Initial STate function 60) is used, the followin
g
state
devices are automaticall
y
assi
g
ned operations which cannot be chan
g
ed directl
y
b
y
a
users pro
g
ram:
S0 : Manual operation initial state
S1 : Zero return initial state
S2 : Automatic operation initial state
S10 to S19 : Allocated for the creation of the zero return pro
g
ram sequence
Monitoring STL programs:
• To monitor the d
y
namic-active states within an STL pro
g
ram, special auxiliar
y
rela
y
M8047 must be driven ON.
STL/SFC programming:
• For more information on STL/SFC st
y
le pro
g
rammin
g
, please see chapter 3.
IST instruction:
• For more information on the IST instruction please see pa
g
e 5-67.
S2
X0
X1
X2
X3
1
S20
S21
S22
Y0
Y1
Y2