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4.A2CCPU
- - - - - - - - - - - - - - - - - - - - MELSEC·A
I
WDT error occurs If the
WOT counter value exceeds
the .etting
I
Sequence program operat1ion
1
~ND
pro6eSsing time
Scan time (WDT counting value)
I
o
END
1
I
L
WDT reset (WDT Is reset
when END is executed)
END
0
END
==1.-I=======I-t=======-
Fig. 4.7 Resetting Watch Dog Timer
(4)
Watch dog timer error processing
Do one of the following if the scan time of a sequence program is greater
than the watch dog timer setting.
(a) Change the sequence program so that the operation time is within
the watch dog timer setting.
(b) Change the watch dog timer setting.
Setting range: 0 to 2000 msec
(c) Reset the watch dog timer with the
wor
instruction in the sequence
program.
The watch dog timer is reset at the time the WOT instruction is
executed and it begins counting again from "0·.
Note that the scan time values registered in 09017 to 09019 are not
reset when the WOT instruction is executed.
POINT
I
(1) The watch dog timer setting must be as indicated below if constant
scan (see Section 4.2.1) is set.
I
Constant scan setting
+
10 msec s Watch dog timer setting
I
(2) When the A2C stops communication with a remote terminal module.
the output state of the remote module is as follows:
(a) A2C I/O module
: all turns OFF
(b) Remote I/O module for MINI-53: depends on EC mode setting
4-12

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