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3.3 Latch Function
This function holds data in each device of the CPU module when:
• the CPU module is powered off and then on,
• the CPU module is reset, or
• power failure occurs exceeding the allowable momentary power failure time.
Data in devices of the CPU module are cleared and set back to their default (bit device: off, word device: 0) if the latch
function is not used.
(1) Application
This function is used to hold the data managed by sequential control and continue control operation especially
when the CPU module is powered off and then on.
(2) Program operation when the latch function is used
Program operation is the same, regardless of the latch status.
(3) Devices that can be latched
The following devices can be latched. (By default, only the latch relay is latched.)
• Latch relay (L)
• Link relay (B)
• Annunciator (F)
• Edge relay (V)
•Timer (T)
• Retentive timer (ST)
• Counter (C)
• Data register (D)
• Link register (W)
The following devices also can be latched when the file register is set to be used in parameter (PLC file tab).
• File register (R, ZR)
• Extended data register (D)
• Extended link register (W)
When the battery life-prolonging function ( Page 249, Section 3.26) is set, the latch relay cannot be latched.
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