Mitsubishi Electric QJ71C24N-R4 - The RD LED Does Not Blink Even after Message Transmission from the External Device

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MELSEC-Q
11 TROUBLESHOOTING
11.3.2 The "RD" LED does not blink even after message transmission from the external
device.
Symptom Cause Corrective action
MC
Bidirectional
Non
procedure
Pre-defined
• "RD" does not blink
even through an
external device is
transmitting a
message.
• Signal lines are not
connected correctly.
• Check if the Q series C24 and external
RD(RXD) and SD(TXD) signal lines are
cross connected.
• Use the external device OPEN statement to
check if the opened port and the cable
connection port are matched.
• External device
transmission control
signals are not turned
ON.
• Connect the wiring so that the "DR(DSR)",
"CS(CTS)", and other transmission control
signals are ready.
Note
• Since the control signal specifications
depend on the device, connect the wiring
by seeing the instruction manual of the
device used.
• If the message
passes through an
RS-232
RS-422
converter, modem,
etc., the signal is
interrupted at one of
the intervening
devices.
• Check the specifications of the converter
and modem and recheck the settings and
wiring