Mitsubishi MELSEC LJ71C24, User Manual

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15 TROUBLESHOOTING
15.3.15 Whether the communication error is caused on the C24 or external device is unclear
Symptom Cause Corrective action MC
Bi
di
re
ct
io
na
l
N
on-
procedural
Predefined
• Whether the
communications error
cause is in the C24 or
an external device is
unclear.
⎯
• Test the C24 as described below to check
where the cause is.
1) Check the hardware.
• The C24 must be installed firmly.
• The pins of the C24 must not be bent or
otherwise abnormal.
2) Test the C24 alone. (Refer to Section 6.4.)
• ROM/RAM/switch test must not
generate any errors.
• Self-loopback test must not generate
any errors.
3) Check the state of the CPU module.
• There must not be any errors that stop
the CPU module operation.
Note
• The following methods are available for
testing if normal communications are
possible with the C24 alone.
1) With one C24, set CH1 and CH2 to the
nonprocedural 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 C24 are available, set one
C24 to the nonprocedural protocol and
the other C24 to the MC protocol and
transmit an MC protocol message from
the nonprocedural protocol station. If the
MC protocol station returns the transmit
message normally, transmit and receive
processing is normal.