Latch Relays (L) - Mitsubishi Electric MELSEC-Q Series User Manual

10 DEVICES

10.2.4 Latch relays (L)

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(1) Definition
(a) Latch relays are auxiliary relays which can be latched by the programmable
controller's internal latch (memory backup).
Latch relay operation results (ON/OFF information) are saved even in the
following cases:
• When power is switched from OFF to ON.
• When a Basic model QCPU reset occurs.
The latch is backed up by the Basic model QCPU battery.
(b) Performing remote latch clear using GX Developer turns OFF the latch
relay. However, the latch relay that has been set to "Latch (2): Cannot be
cleared by latch clear" in the device setting PLC parameters cannot be
turned OFF if remote latch clear is performed.
(c) There are no restrictions regarding the number of contacts (N/O contacts,
N/C contacts) used in the program.
X0
L0
X1 L0
X2 L0
(2) Procedure for external outputs
Outputs (Y) are used to output sequence program operation results to an
external destination.
REMARK
Internal relays (M) should be used when a latch (memory backup) is not required.
See Section 10.2.3 for details regarding internal relays.
No restrictions regarding the quantity used.
L0 switches ON at X0 OFF to ON.
SET L0
The latch relay (L0) ON can only be used for internal
Basic model QCPU processing, and cannot be output
externally.
K20
T0
Y20
L0 ON/OFF information is output from the output
module to an external destination.
L100
L2047
Figure 10.6 Latch Relay
MELSEC-Q
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