Latch Functions - Mitsubishi Electric MELSEC-Q Series User Manual

7 FUNCTION

7.3 Latch Functions

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(1) What is Latch Functions?
(a) The values of each Basic 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 is a function to maintain the device details when the above conditions
occur.
The availability of latches does not affect the operation performed by a
program.
(b) Latch can be used to maintain the production count, defective count,
address and other data to continue control if the PLC is powered OFF, reset
operation is performed, or an instantaneous power failure occurs for longer
than the permissible time during management of the above data for
continuous control.
(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 with the PLC parameter mode device
setting.
Latch range setting can be made in two ranges: latch clear (remote latch clear
operation) valid range and invalid range.
MELSEC-Q
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