10 TROUBLESHOOTING

MELSEC-Q

10.3.4Troubleshooting when an external device transmitted a message and "RD" LED blinked, but the Read Request signal was not turned ON

Symptom

Cause

 

 

 

Corrective action

MC

 

 

• Check if the communication protocol is set correctly.

 

 

 

•

Check if the mode was switched without using the

 

 

• Communication protocol

 

buffer memory mode switching area.

 

 

 

Note

 

 

 

is set incorrect.

 

• The communication protocol setting contents and

 

 

 

 

 

the communication protocol in the current operation

 

 

 

 

 

can be checked at buffer memory addresses 250H

 

 

 

 

 

to (CH1) and 260H (CH2).

 

 

• When "Check CD

• Since messages are skipped when the CD terminal is

 

 

 

turned OFF when "Check CD terminal" is set, change

 

 

terminal" was set, the CD

 

 

 

 

the wiring so that the CD terminal remains on all the

 

 

terminal was turned off.

 

time.

 

 

• When DC control is

•

Check if a message is transmitted without transmitting

 

 

 

"DC1 (11H)" after the external device transmits "DC3

 

 

selected, the necessary

 

 

 

 

(13H)" during DC1/DC3 external control.

 

 

DC codes are not

•

Check if the next message is transmitted without

 

 

 

adding "DC2 (12H)" after the external device transmits

 

 

transmitted.

 

 

 

•

"DC4 (14H)" during DC2/DC4 external control.

 

• An external device

• The end code was not

Check if the end code set at the Q series C24 and the

 

 

end code transmitted from the external device are the

 

received, or fixed length

 

 

transmitted a message

 

same.

 

data was not received.

•

 

and "RD" blinked, but

Check if the external device transmitted the fixed

 

 

•

length designated at the Q series C24.

 

the read request signal

 

Check if the trailer frame was transmitted during

 

(X0) was not turned

 

 

communications by user frame.

 

 

 

Note

 

 

ON.

 

 

 

 

 

 

•

When the send data from the external device is

 

 

 

 

correct, take the corrective action described in

 

 

 

 

Sections 10.3.10 and 10.3.11.

 

 

• The Q series C24

• The data count basics, message format, etc. depend

 

 

 

on the following settings.

 

 

setting and message

 

 

 

 

⋅

ASCII-BIN conversion enable/disable

 

 

format do not match.

 

⋅

Transparent code setting

 

 

 

 

⋅

User frame setting

 

 

 

 

See the relevant section for a description of operation

 

 

 

 

according to the set contents and setting of each item.

 

 

 

• Set, or shorten, the monitoring time and retransmit the

 

 

• The Q series C24 data

 

message from the external device and determine the

 

 

 

trouble from the contents of the time-out error.

 

 

communications

 

Note

 

 

 

monitoring time is set to

 

•

Error detection by the watchdog timer (timer 0 to

 

 

 

 

timer 2) is possible in the following cases.

 

 

"infinite", or the

 

 

 

 

 

 

⋅

When part of a message is skipped.

 

 

monitoring time is too

 

 

⋅

When transmission from an external device is

 

 

long.

 

 

 

interrupted.

 

 

 

 

See Chapter 6 of User's Manual (Application) for a

 

 

 

 

 

 

 

 

 

 

detailed description of the monitoring time.

 

Bidirectiona Non procedure

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