10 TROUBLESHOOTING

MELSEC-Q

10.3.11 Troubleshooting when communications is intermittently established and lost

 

Symptom

 

Cause

 

Corrective action

MC

 

 

• With a multidrop link, two or

• Connect the external devices and the Q series C24 in a

 

 

 

 

more devices transmitted

 

1:1 configuration and perform a communications test.

 

 

 

 

data at the same time.

 

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.

 

 

 

•

The signal cable wiring

 

 

 

 

 

 

connection is faulty.

• Replace the cable, or make the connections firm.

 

• Communications are

• When "Check CD terminal"

• Change the wiring so that the CD signal remains ON all

 

 

is set, the CD signal is

 

the time, or change the setting to "Do not check CD

 

intermittently established

 

 

 

 

turned on/off repeatedly.

 

terminal".

 

and lost.

 

 

 

• When half-duplex

 

 

 

(

1)

•

Control the external device so that the ON/OFF timing

 

 

communications is selected,

 

 

 

 

the ON/OFF timing of each

 

of each signal is matched.

 

 

 

 

 

See Chapter 8 of User's Manual (Application).

 

 

 

 

signal is not matched.

 

 

 

 

 

 

 

 

 

 

• Requested processing of the

 

 

 

 

 

 

next transmission before the

 

 

 

 

 

 

processing of the current

 

 

 

 

 

 

transmission is completed.

•

Make sure to obtain handshake in the sequence

 

 

 

• Requested processing of the

 

program.

 

 

 

 

next reception before the

 

 

 

 

 

 

processing of the current

 

 

 

 

 

 

reception is completed.

 

 

 

Bidirectional

Non procedure

 

 

1 The following explains how to take corrective actions when a normal exit response message cannot be received upon sending of a command message.

1)When a response message of abnormal end is received

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 (see Section 10.2).

2)When response messages cannot be received

Change the setting value for the response monitoring time (timer 1, default value is 5 seconds).

(See Section 6.2 of the User's Manual (Application).)

If response messages still cannot be received after changing the setting value, check the communication protocol setting of the corresponding interface, the ON status of the displayed LED, and the connection cable.

3)When the first part of a response message cannot be received

Increase the setting value of the message wait time (the default value is 0 ms). (See Section 6.4 of the User's Manual (Application).)

If response messages still cannot be received after increasing the setting value, it is necessary to reduce the processing time from the end of transmission processing to the start of reception processing on the external device side.

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