Mitsubishi MELSEC LJ71C24, User Manual

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15 TROUBLESHOOTING
15.3.13 Communication is intermittent
Symptom Cause Corrective action MC
Bi
di
re
ct
io
na
l
Non-
proc
edur
al
P
redef
ined
• With a multidrop link, two or
more devices transmitted
data at the same time.
• Connect the external devices and the C24 in a 1:1
configuration and perform a communications test.
Since data is transmitted simultaneously from two or
more devices with a multidrop link when normal
communications among all the devices is possible,
interlock the external devices so that they do not
transmit simultaneously.
• The signal cable wiring
connection is faulty. • Replace the cable, or make the connections firm.
• When "Check CD terminal" is
set, the CD(DCD) signal is
turned on/off repeatedly.
• Change the wiring so that the CD(DCD) signal
remains ON all the time, or change the setting to "Do
not check CD terminal".
• When half-duplex
communications is selected,
the ON/OFF timing of each
signal is not matched.
• Control the external device so that the ON/OFF
timing of each signal is matched.
Refer to User's Manual (Application).
• Requested processing of the
next transmission before the
processing of the current
transmission is completed.
• Requested processing of the
next reception before the
processing of the current
reception is completed.
• Make sure to obtain handshake in the sequence
program.
• Communication via modem
is disrupted.
• Since communication via modem may be disrupted
due to low line quality or instantaneous interruption,
create a sequence program for reconnecting the line
in case of unexpected line disruption.
If this symptom occurs frequently, reduce the
communication speed of the modem, and retry the
communication.
• Communications are
intermittently
established and lost.
( 1)
• The data sent from the C24
are received back on the
RS-422/485 interface (CH2)
side. • Disable the echo back in the Echo back
enable/disable setting before communication.
1 The following explains how to take corrective actions when a normal exit response
message cannot be received upon sending of a command message.
(a) When a response message of abnormal end is received
1) When an external device sent a command message and received an
abnormal end response message, take corrective action with the error
according to the error code in the response message (refer to Section
15.2.2).