Mitsubishi Electric MELSEC iQ-RJ71C24-R4 - SD LED Does Not Flash Even after a Send Request was Made; RD LED Does Not Flash Even Though the Target Device Is Transmitting a Message

27 TROUBLESHOOTING
27.3 Troubleshooting by Symptom
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27
SD LED does not flash even after a send request was made
RD LED does not flash even though the target device is
transmitting a message
Symptom Cause Corrective action MC Non Bi Pd
SD LED does not flash even
after a send request was
made.
The CS(CTS) signal is in the
OFF-state, and C24 cannot
transmit data to the external
device.
• While the CS(CTS) signal is OFF, C24 does not transmit
data to the target device.
Connect so that it is constantly ON when the target device is
ready to receive data.

Due to the transmission
control (DTR control, DC
control), the external device
cannot receive data.
• Wait until the external device is ready to receive data.
• Check the external device or the cable condition when it
takes too long for the external device to be ready to receive
data.

Symptom Cause Corrective action MC Non Bi Pd
RD LED does not flash even
though the target device is
transmitting a message.
Signal lines are not connected
correctly.
• Cross-connect the RD(RXD) and SD(TXD) signals between
C24 and the target device.
• When using MX Component, match the port opened by the
OPEN statement of the target device with the cable
connection port.

The transmission control
signals on the target device
side have not turned ON.
• Connect the wiring so that the transmission control signals
including DR(DSR) and CS(CTS) are ready.
■Remarks
The Specifications of control signal vary depending on the
device. Perform the wiring in accordance with the instruction
manual of the device used.

If the message passes
through a modem or others,
the signal is interrupted at the
side of device relaying the
message.
• Check the specification of the modem to review the settings
and wiring, and correct them if necessary.
