460
27 TROUBLESHOOTING
27.3 Troubleshooting by Symptom
No response message is returned even though the target device
transmitted a message and the RD LED flashes
Symptom Cause Corrective action MC Non Bi Pd
The target device transmitted
a message and RD LED
flashes, but C24 does not
return the response
message.
Communication protocol
setting is incorrect.
• Review the communication protocol setting.
• Review the program whether unintended mode switching is
performed when the buffer memory mode switching area is
used for mode switching.
■Remarks
The communication protocol setting contents and the
communication protocol currently in operation can be checked
at the following addresses.
• 'Communication protocol status (parameter setting)'
(Un\G592/608) set by the parameter
• 'Communication protocol status (current)' (Un\G594/610)
currently in operation
The CD terminal has been
turned OFF when the CD
terminal check is enabled.
• Change the wiring so that the CD terminal remains ON all
the time since a message is initialized (skipped) if the CD
terminal is OFF when the CD terminal check is set to be
enabled.
The header byte of the
message is not data needed
for the set protocol and
format.
Check the data transmitted from the target device with the
Circuit Trace function of Engineering tool, and take the
following corrective actions.
• If the format of message sent from the target device does
not match with the respective protocol and format, correct
the massage format according to the relevant protocol and
format used.
■Remarks
C24 skips all the messages transmitted until the header byte
specified for each protocol and format (for example,
"ENQ(05H)" for format 1) is received.
C24 station number setting
and message station number
designation do not match.
Check the data transmitted from the target device with the
Circuit Trace function of Engineering tool, and take the
following corrective actions.
• Match the station number setting of C24 with the station
number designation of the message.
■Remarks
C24 performs the data reception processing when the station
No. designation is the host station after the header byte
specified for each protocol and format is received.
The C24 data
communications monitoring
time is set to "Unlimited wait",
or the monitoring time is too
long.
• Set or shorten the monitoring time and retransmit the
message from the target device and determine the trouble
from the contents of the time-out error.
■Remarks
Error detection by the monitoring time (timer 0 to timer 2) is
possible in the following cases.
• When part of a message is skipped.
• When transmission from the target device is interrupted.
• A link error occurred when accessing to the other station via
CC-Link IE Controller Network or CC-Link IE Field Network.
For details of the monitoring time, refer to the following
manual.
Page 227 CHANGING DATA COMMUNICATION
MONITORING TIME
The route setting of the
access target CPU module is
incorrect.
• Check the route of the access target CPU module, and set
the route again.
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