4.A2CCPU
--------------------
MELSEC·A
4.2.2
Power failure compensation
for
device data In the A2C (LATCH function)
Each individual device of the A2CCPU is reset when
the
A2CCPU is powered I
up. Device will be cleared when a momentary power failure
occurs
for
more
than 20 msec. After being reset or cleared, all device data is reset
to
the
default values (OFF
for
bit devices and 0
for
word devices).
The latch function retains
the
device data in
the
event
that
the
A2CCPU is
reset by
turning
on
the power or pressing using the RUN switch or a
momentary power failure occurs
for
more
than
20 msec.
Sequence program operation is
the
same whether
the
data is latched or not.
(1) Applications
The latch function is used to continue the control by retaining
data
such
as
the
number
of
completed
products,
the
number
of
defective
products,
and
the addresses should a momentary power failure
occur
for
more than 20 msec.
(2) Latch devices and latch range setting
(a) The devices whose data can be latched are listed
below:
1) Latch relay
(LO
to L2047)
2) Link relay
(BO
to B3FF)
3) Timer
(TO
to T255)
4) Counter
(CO
to C255)
5) Data register
(DO
to 01023)
6) Link register
(WO
to
W3FF)
(b) The latch range is set in
the
peripheral parameters
per
device.
POINTI
Device date within the latch range is backed by
the
battery (A6BAT)
installed on the A2C.
(1) The battery is required even when the operation is performed using a
ROM which stores the sequence program.
(2) Device data within the latch range is destroyed if
the
battery
connector
is disengaged from the A2C when
the
A2C is
being
turned off.
4-22
•
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