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Troubleshooting Section 9-3
9-3-3 I/O Link Problems
Use the following table to troubleshoot I/O Link problems.
The DeviceNet Unit’s MS indicator is ON and
green, but the NS indicator continues to flash
green.
(The NS indicator normally goes ON 2 s after
the MS indicator.)
• If the DeviceNet Unit’s 7-segment display is displaying an error code,
refer to the tables in 9-1 Troubleshooting with the DeviceNet Unit In-
dicators.
• Restart the Unit. Replace the Unit if it doesn’t restart.
The DeviceNet Unit’s MS and NS indicators are
ON and green, but the 7-segment display contin-
ues to flash the master’s node address.
(The node address normally stops flashing
within 8 s after the NS lights.)
• Check that the DeviceNet Unit’s baud rate matches the baud rates set
on all of the slaves. If they don’t match, set all of the baud rates to the
same value.
• Make sure that there are121-Ω terminators connected at both ends
of the trunk line. Connect 121-Ω terminators if the wrong resistance
is being used.
• Check whether all of the slaves’ settings are correct.
• Check whether the communications cables are wired correctly.
• Check whether the power supply cables and power supply are wired
and set correctly.
• Check for broken wires in the communications and power supply ca-
bles attached to the connectors.
• Check whether the slaves are operating properly.
When an OMRON slave is being used, refer to the DeviceNet Slaves
Operation Manual (W347).
• If another company’s slave is being used, refer to that slave’s user’s
manual.
Error Probable cause
Error Probable cause
The I/O isn’t simultaneous. Observe the following precautions when writing application programs:
• The simultaneity of node-units of data is ensured between the PC and
DeviceNet Unit.
• In OMRON slaves, the simultaneity of word-units of data is ensured.
• If another company’s slave is being used, refer to that slave’s user’s
manual for details.
At startup, OFF outputs are output from the
slaves.
When the master is operating in scan list enabled mode and the PC is
set to maintain the status of I/O area bits, those held output points will
be output from the output slaves at startup.
Be sure to perform the Create Scan List operation and operate the
master with the scan list enabled.
Refer to the CS1 Series CPU Unit Operation Manual (W339) or the CJ
Series CPU Unit Operation Manual (W393) for details on maintaining I/
O area data with the IOM Hold Bit.