Omron NJ501-1 Series User Manual page 342

Appendices
 Restrictions
If a short-circuit occurs in an external load, immediately turn OFF the corresponding output and
remove the cause. An alarm output bit that corresponds to the external load output number is turned
ON. There is an alarm output bit for every common.
When an alarm output bit turns ON, use a self-holding bit for the alarm in the user program and turn
OFF the corresponding output.
The Alarm Output Bits are allocated in the Basic I/O Unit Information Area system-defined variable.
Sixteen output bits are assigned for each slot and rack in which a Unit is mounted.
_CJB_IOUnitInfo[rack_number,slot_number,serial_number_in_Unit]
For example, when the CJ1W-OD212 is mounted in slot 0 of rack 0, _CJB_IOUnitInfo[0,0,0]
changes to TRUE if output Ch1Out2 changes to TRUE.
When the CJ1W-OD232 is mounted in slot 1 of rack 2, _CJB_IOUnitInfo[2,1,1] changes to TRUE if
output Ch2Out8 changes to TRUE.
A-100 NJ-series CPU Unit Hardware User's Manual (W500)