Mitsubishi MELSEC LJ71C24, User Manual

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15 TROUBLESHOOTING
15.3.2 The "RD" LED does not blink even after message transmission from the external
device
Symptom Cause Corrective action MC
Bidi
rectio
nal
N
on-
procedural
Predefined
• Signal lines are not
connected correctly.
• Check if the 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.
• "RD" does not blink
even through an
external device is
transmitting a
message.
• If the message
passes through a
modem or others, the
signal is interrupted at
one of the intervening
devices.
• Check the specification of the modem and
recheck the settings and wiring