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7 FUNCTION
7.3 Latch Functions
7 - 5
(1) What is Latch Functions?
(a)
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 power is turned on.
• The reset operation is performed.
• There is a momentary power failure for more than the permissible amount
of time.
Latch function maintains the device information when the above conditions
occur.
The availability of latches does not affect the operation performed by a
program.
(b)
The latch can be used to continue control by maintaining the production
quantity, defect count, and address even when there is a momentary power
failure for more than the permissible amount of time.
(c)
The following devices can use the latch function:
(The default latch range is only the latch relay.)
1)
Latch relay(L)
2)
Link relay(B)
3)
Annunciator(F)
4)
Edge relay(V)
5)
Timer(T)
6)
Retentive timer(ST)
7)
Counter(C)
8)
Data register(D)
9)
Link register(W)
(2) Latch Range Setting
The latch range setting is performed at the "Device" tab screen in the "(PLC)
Parameter" dialog box.
There are two types of range in which the latch clear key (RESET/L.CLR switch)
and remote latch clear operation become valid or invalid in the latch range
setting.
MELSEC-Q
7 - 5
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