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MELSEC-Q
10 TROUBLESHOOTING
REMARK
The following are precautionary notes when exchanging data with an external device
via one of the Q series C24 interfaces.
(1) When the power supply to the Q series C24 or external device is started, the
remote device that is connected may generate a reception error.
(2) If the remote device that is connected starts up while data is being transmitted,
the remote device side will generate a reception error.
(3) When the Q series C24 error LED lights up because a reception error has
occurred, turn off the light if necessary in accordance with Section 10.1.
Also, if a reception error has occurred on the external device side, handle the
error by seeing to the operating manual for the external device.
Handle the occurrence of a reception error on the Q series C24 side using
the following corrective actions.
• When communicating with the MC protocol
The Q series C24 will disregard the received data or returns a response
message indicating an abnormal termination if it detects a reception error
after receiving the head data of the command message in the set format.
If the reception error is detected before the head data of the command
message in the set format is received, the received data will be
disregarded.
• When communicating using non procedure protocol
If the Q series C24 detects a reception error, the reception abnormal
detection signal (X4, XB) turns ON.
Perform procedures such as detection of reception error or clearing
received data as required by following the explanations found in Sections
6.1.4 and 6.1.5.
• When communicating using bidirectional protocol
When the Q series C24 detects a reception error after the head data of a
communication message for bidirectional protocol is received, it returns a
response message indicating an abnormal termination.
If the reception error is detected before the head data of the
communication message for bidirectional protocol is received, the
received data will be disregarded.