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7.4 Precautions at System Switching Occurrence
7
PROGRAMMING CAUTIONS
When outputting the output (Y) or writing buffer memory to a module or
external device, consider time required for tracking transfer from the control
system CPU module to the standby system CPU module.
The program example to output, delaying one scan from the time up of the
timer, is shown in Diagram 7.20.
[Program example]
(Before measures)
(After measures)
POINT
Set [Do tracking] at [Signal flow memory tracking setting] on [Tracking settings] in
redundant parameter.
(3) Precautions regarding writing data from the GOT and external device
etc.
Pay attention to the following points regarding writing data from the GOT and external
device etc.
1) The tracking data may not be reflected to the new control system CPU module
depending on the timing of the system switching occurrence such as turning
power supply OFF.
In this case, data written immediately before switching systems by the GOT or
external device may disappear. Rewrite data after switching systems.
Diagram 7.20 Program Example when Outputting by timer contact
T0
SET Y10
T10
RST Y10
Delays SET Y10 by one
scan from PLS M1.
Delays RST Y10 by one
scan from PLS M11.
M1
SET Y10
T0
PLS M1
M11
RST Y10
T10
PLS M11
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