Mitsubishi MELSEC QJ71C24, User Manual

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MELSEC-Q
11 TROUBLESHOOTING
11.3.3 No response message is returned even though the external device transmitted a
message and the "RD" LED blinked.
Symptom Cause Corrective action
MC
B
idi
rec
tional
Non proc
edure
P
re-def
ined
• Communication protocol is
set incorrectly.
• 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
/260
H
).
• When "Check CD
terminal" was set, the CD
terminal was turned OFF.
• Since the message is initialized (skipped reading)
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.
• The header byte of the
message is not data
needed by the set protocol
and format.
• Check if the external device sent a message matched
to the protocol and format.
• Use the communication monitoring function to check
the message from the external device.
Note
• The Q series C24 skips all the messages transmitted
until the header byte set for each protocol and format
(for example, "ENQ (05
H
)" for format 1) is received.
• The Q series C24 station
No. switch setting and
message station No.
designation do not match.
• Check the Q series C24 station No. setting and
message station No. designation.
• Use the communication monitoring function to check
the message from the external device.
Note
• When the station No. designation is local station
after the header byte set for each protocol and format
is received, the Q series C24 performs receive
processing.
• 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 watchdog timers (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.
• When a link error was generated while accessing
another station over a CC-Link IE Controller
Network, CC-Link IE Field Network,
MELSECNET/H, MELSECNET/10.
See User's Manual (Application) for a detailed
description of the monitoring time.
• An external device
transmitted a message
and "RD" blinked, but
the Q series C24 did
not return a response
message. ("NEU"
remains on and "SD"
does not blink)
• The path setting of the
programmable controller
CPU to be accessed is
incorrect.
Check the path of the programmable controller CPU to
be accessed and set the path again.