4.
AXCPU
/MELSEC-A
(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: 10 to
2000
ms
(c) Reset the watch dog timer with the
ml
instruction
in
the sequence program.
The watch dog timer is reset
at
the time the
instruction is executed and
it
begins counting again from
"0".
Note
that
the scan time values
DM19 are not reset when the
executed.
POINT
I
I
I
The watch dog timer setting must
be
as
indicated below
if
constant scan
(see
4.2.1)
is
set.
Y
d
1)
*
.........
An infinite loop may be caused if
a
program execution sequence
is
jumpes to a smaller step number because of a
CJ
instruction.
T=I
Example:
An infinite loop is caused if there is no jump
instruction calling for a jump to a step
beyond step
CJ
W
to between point
W
and
step
CJ
PO,
thereby precluding the execution
CJW
of the instruction.
2)
Data stored in special registers
D9017
to
9019
a)
09017
.........
Smallest value of scan time
b)
DW18
.........
Present value of scan time
c)
m1g
.........
Largest value of scan time
?l
a
d
1
i
4
Y
n
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