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14 LATCH FUNCTION
14.1 Types of Latch
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14 LATCH FUNCTION
The contents of each device/label of the CPU module is cleared in the cases described below and changed to its default
value.
• At power OFFON of the CPU module
• At reset
• A power failure that exceeded allowable momentary power interruption
The contents of each device/label with latch setting will be maintained in case of power failure even in the above-mentioned
cases. Therefore, when the data is managed by continuous control, even if power of the CPU is turned OFF or there is a
power failure that exceeds the allowable momentary power interruption, all data can be maintained and control can be
continued.
14.1 Types of Latch
There are two types of latches, latch (1) and latch (2).
Latch clear range can be set by selecting latch (1) or latch (2).
For latch clearing, refer to Page 101 Clearing of Data of the Latch Range.
14.2 Device/label that can be Latched
The devices and labels that can be latched are described below.
The devices that can be latched
The devices that can be latched are described below.
*1 Link register (W) and file register (R) can be latched only when an optional battery is used.
Labels that can be latched
The labels that can be latched are described below.
*1 Only sub-routine type FB can be used.
Device Specification Method Applicable latch type
Internal relay (M) Specify the latch range Latch (1) or Latch (2)
Latch relay (L) Specify the number of points Latch (2) only
Link relay (B) Specify the latch range Latch (1) or Latch (2)
Annunciator (F) Specify the latch range Latch (1) or Latch (2)
Step relay (S) Specify the latch range Latch (1) only
Timer (T)/Accumulation timer (ST) Specify the latch range Latch (1) or Latch (2)
Counter (C)/Long counter (LC) Specify the latch range Latch (1) or Latch (2)
Data register (D) Specify the latch range Latch (1) or Latch (2)
Link register (W)
*1
Specify the latch range Latch (1) or Latch (2)
File register (R)
*1
Specify the latch range Latch (1) or Latch (2)
Label Type Attribute Data type
Global label VAR_GLOBAL RETAIN Basic data type, array, structure
Local label of the program block VAR
Local label of the Function Block VAR
VAR_INPUT
*1
VAR_OUTPUT
VAR_PUBLIC