Omron CJ1W-PRT21 Operation Manual page 71

Troubleshooting
Table 12 I/O data communication problems (continued)
Description
The COMM LED is Another Special I/O Unit makes use of
ON, but no I/O data the same data area(s).
is exchanged with
the PLC.
The slave operates in 'Sync' or 'Freeze' -
mode.
WatchDog is off
Slave Unit is defective.
No I/O data is Slave is not connected properly.
exchanged with the
PROFIBUS master
The master unit or the transmission line
have failed, the watchdog of the slave
has switched the outputs of the slave to
the fail-safe state.
SIOU refresh is disabled.
Slave Unit is defective.
52
Possible cause Possible remedy
Check the mapping of the Unit and other Special I/O
Units. If they overlap, then one Unit overwrites the data
area of the other Unit and makes it look like that no
data is being exchanged with the PLC. If an overlap
exists, the Unit's DM settings should be changed.
In these modes, the I/O data is only updated after
another transmission of the 'Sync' or 'Freeze' com-
mand. If this is not desired, these modes should be
turned OFF by the master (Unsync / Unfreeze). Check
CIO n at master side.
Enable Watchdog.
Replace the CJ1W-PRT21.
Check the slave's connection to PROFIBUS. Are the
correct pins connected, is the shield also connected, is
the bus length not exceeded?
Check the transmission line and master unit or disable
the slave's watchdog (recommended for troubleshoot-
ing only).
Check PLC settings.
Replace the CJ1W-PRT21.
Section 5-2