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6.3 Latch Function
6
FUNCTIONS
6.3 Latch Function
(1) Definition of Latch Functions
The values of each High Performance model QCPU device are set back to the default
(bit device: OFF and word device: 0) when;
• The PLC is powered OFF and then ON
• The reset operation is performed.
• Power failure longer than the permissible momentary power failure time occurs
Latch function maintains the device information when the above conditions occur.
(2) Operation performed when latch is used
Program operation is the same, independently of whether latch is used or not.
(3) Applications of latch function
Latch can be used to hold the data, which is being managed by continuous control, to
continue control if the PLC is powered OFF, reset operation is performed, or a power
failure longer than the permissible momentary power failure time occurs.
(4) Devices that can be latched
The following devices can be latched.
(By default, only the latch relay is enabled for latch.)
• Latch relay(L)
• Link relay(B)
• Annunciator(F)
• Edge relay(V)
•Timer(T)
• Retentive timer(ST)
• Counter(C)
• Data register(D)
• Link register(W)
POINT
When the battery life-prolonging function (Universal model QCPU only) is set, the
latch relay cannot be latched.
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