FX Series Programmable Controllers Points Of Technique 10
10-13
Points of interest:
a) Users of the IST instruction will be aware that only one of the operation modes should be
active at one time. In this example program the isolation of 'Manual' and 'Zero return'
modes by the use of separate DU control screens, and the use of a rotary switch to
isolate the three automatic modes achieves this objective. Alternatively all of the
operation modes could be selected by a rotary switch.
b) For users who would like to test this example using simulator switches (i.e., without using
a data access unit) the appropriate program changes are noted next to the full program
listing later in this section. Alternatively, the original program could be used with all of the
input conditions being given by forcing ON the contacts with a programming device e.g.
a hand held programmer, Medoc etc.
c) Special flags used in this program are:
• M8040: State transfer inhibit
- Manual mode: Always ON.
Zero return and Cycle modes: Once the 'Stop' input is given the current state is
retained until the 'Start' input is received.
Step mode: This flag is OFF when the 'Start' input is ON. At all other times M8040 is
ON, this enables the single STL step operation to be achieved.
Auto mode: M8040 is ON initially when the PLC is switched into RUN. It is reset
when the 'Start' input is given.
• M8041: State transfer start
- Manual and Zero return modes: This flag is not used.
Step and Cycle modes: This flag is only active while the 'Start' input is received.
Auto mode: The flag is set ON after the 'Start' input is received. It is reset after the
'Stop' input is received.
• M8042: Start pulse
- This is momentarily active after the 'Start' input is received.
• M8043: Zero return complete
- This is a user activated device which should be controlled within the users program.
• M8044: At Zero position/ condition
- This is a user activated device which should be controlled within the users program.
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