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MELSEC-Q
10 TROUBLESHOOTING
10.3.13 Troubleshooting when it is unclear whether the communication error cause is in the
Q series C24 or an external device
Symptom Cause Corrective action MC
Bidirectional
Non
procedure
• Whether the
communications error
cause is in the Q series
C24 or an external
device is unclear.
• Test the Q series C24 as described below to
check where the cause is.
1) Check the hardware.
• The Q series C24 must be installed firmly.
• The pins of the Q series C24 must not be
bent or otherwise abnormal.
2) Test the Q series C24 alone. (See Section
4.7.)
• ROM/RAM/switch test must not generate
any errors.
• Self loopback test must not generate any
errors.
3) Check the state of the PLC CPU.
• There must not be any errors that stop
PLC CPU operation.
Note
• The following methods are available for
testing if normal communications are possible
with the Q series C24 alone.
1) With one the Q series C24, set CH1 and
CH2 to the non procedure protocol and
connect the wiring the same as for the self
loopback test and transmit data from one
channel and receive the transmitted data
at the other channel. If the transmitted
data and the received data are the same,
transmit and receive processing is
performed normally.
2) When two Q series C24 are available, set
one Q series C24 to the non procedure
protocol and the other Q series C24 to a
dedicated protocol and transmit an MC
protocol message from the non procedure
protocol station. If the MC protocol station
returns the transmit message normally,
transmit and receive processing is
normal.