Omron CJ - REFERENCE MANUAL 10-2009 Reference Manual page 14

Using the Unit Version
Labels
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Unit version
Use the above display to confirm the unit version of the CPU Unit connected
online.
The following unit version labels are provided with the CPU Unit.
These labels can be attached to the front of previous CPU Units to differenti-
ate between CPU Units of different unit versions.
CS/CJ/NSJ Series Instructions Reference Manual (W474)