Communication Is Intermittent - Mitsubishi Melsec-L Series User Manual

15.3.13 Communication is intermittent

Symptom
• With a multidrop link, two or
• The signal cable wiring
• When "Check CD terminal" is
• When half-duplex
• Communications are
intermittently
• Requested processing of the
established and lost.
( 1)
• Requested processing of the
• Communication via modem
• The data sent from the C24
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Cause
more devices transmitted
data at the same time.
connection is faulty.
set, the CD(DCD) signal is
turned on/off repeatedly.
communications is selected,
the ON/OFF timing of each
signal is not matched.
next transmission before the
processing of the current
transmission is completed.
next reception before the
processing of the current
reception is completed.
is disrupted.
are received back on the
RS-422/485 interface (CH2)
side.
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).
Corrective action
• 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.
• Replace the cable, or make the connections firm.
• Change the wiring so that the CD(DCD) signal
remains ON all the time, or change the setting to "Do
not check CD terminal".
• Control the external device so that the ON/OFF
timing of each signal is matched.
Refer to User's Manual (Application).
• Make sure to obtain handshake in the sequence
program.
• 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.
• Disable the echo back in the Echo back
enable/disable setting before communication.
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