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Power Failure Compensation For Device Data In The A2c (latch Function) - Mitsubishi Electric MELSEC-A Series User Manual

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Power failure compensation for device data In the A2C (LATCH function)
Each individual device of the A2CCPU is reset when the A2CCPU is powered
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.
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.
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.


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