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FX Series Programmable Controllers Points Of Technique 10
10-13
Points of interest:
a) Users of the IST instruction will be aware that onl
y
one of the operation modes should be
active at one time. In this example pro
g
ram the isolation of 'Manual' and 'Zero return'
modes b
y
the use of separate DU control screens, and the use of a rotar
y
switch to
isolate the three automatic modes achieves this ob
j
ective. Alternativel
y
all of the
operation modes could be selected b
y
a rotar
y
switch.
b) For users who would like to test this example usin
g
simulator switches (i.e., without usin
g
a data access unit) the appropriate pro
g
ram chan
g
es are noted next to the full pro
g
ram
listin
g
later in this section. Alternativel
y
, the ori
g
inal pro
g
ram could be used with all of the
input conditions bein
g
g
iven b
y
forcin
g
ON the contacts with a pro
g
rammin
g
device e.
g
.
a hand held pro
g
rammer, Medoc etc.
c) Special fla
g
s used in this pro
g
ram are:
• M8040: State transfer inhibit
- Manual mode: Alwa
y
s ON.
Zero return and C
y
cle modes: Once the 'Stop' input is
g
iven the current state is
retained until the 'Start' input is received.
Step mode: This fla
g
is OFF when the 'Start' input is ON. At all other times M8040 is
ON, this enables the sin
g
le STL step operation to be achieved.
Auto mode: M8040 is ON initiall
y
when the PLC is switched into RUN. It is reset
when the 'Start' input is
g
iven.
• M8041: State transfer start
- Manual and Zero return modes: This fla
g
is not used.
Step and C
y
cle modes: This fla
g
is onl
y
active while the 'Start' input is received.
Auto mode: The fla
g
is set ON after the 'Start' input is received. It is reset after the
'Stop' input is received.
• M8042: Start pulse
- This is momentaril
y
active after the 'Start' input is received.
• M8043: Zero return complete
- This is a user activated device which should be controlled within the users pro
g
ram.
• M8044: At Zero position/ condition
- This is a user activated device which should be controlled within the users pro
g
ram.