Mitsubishi Electric QJ71C24N-R4 - Read Request Signal Does Not Turn on Even Though the External Device Transmitted a Message and the RD LED was Blinking

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MELSEC-Q
11 TROUBLESHOOTING
11.3.5 Read request signal does not turn ON even though the external device transmitted a
message and the "RD" LED was blinking.
Symptom Cause Corrective action
MC
Bidirectional
Non
procedure
Pre-defined
• An external device
transmitted a
message and "RD"
blinked, but the read
request signal
(X3/XA) was not
turned ON.
• Communication protocol
is set incorrect.
• Check if the communication protocol is set correctly.
• Check if the mode was switched without using the buffer
memory mode switching area.
Note
• The communication protocol setting contents and the
communication protocol in the current operation can be
checked at communication protocol status (address:
250
H/260H).
• When "Check CD
terminal" was set, the CD
terminal was turned off.
• Since messages are skipped when the CD terminal is
turned OFF when "Check CD terminal" is set, change the
wiring so that the CD terminal remains on all the time.
• When DC control is
selected, the necessary
DC codes are not
transmitted.
• Check if a message is transmitted without transmitting
"DC1 (11
H)" after the external device transmits "DC3
(13
H)" during DC1/DC3 external control.
• Check if the next message is transmitted without adding
"DC2 (12
H)" after the external device transmits "DC4
(14
H)" during DC2/DC4 external control.
• Use the communication monitoring function to check the
message from the external device.
• The end code was not
received, or fixed length
data was not received.
• Check if the end code set at the Q series C24 and the end
code transmitted from the external device are the same.
• Check if the external device transmitted the fixed length
designated at the Q series C24.
• Check if the trailer frame was transmitted during
communications by user frame.
• Use the communication monitoring function to check the
message from the external device.
Note
• When the send data from the external device is correct,
take the corrective action described in Sections 11.3.10
and 11.3.11.
• The Q series C24 setting
and message format do
not match.
• The data count basics, message format, etc. depend on
the following settings.
• ASCII-BIN conversion enable/disable
• 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.
• The Q series C24 data
communications
monitoring time is set to
"Infinite wait", or the
monitoring time is too
long.
• Set, or shorten, the monitoring time and retransmit the
message from the external device and determine the
trouble from the contents of the time-out error.
Note
• Error detection by the watchdog timer (timer 0 to timer 2)
is possible in the following cases.
• When part of a message is skipped.
• When transmission from an external device is
interrupted.
See User's Manual (Application) for a detailed description
of the monitoring time.