Omron WIRED REMOTE I-O System Manual page 42

Unit Numbers and I/O Word Allocation
Example 2: C500 with
Remote Terminals
Master
Because the I/O Units are allocated words starting at the lower end (word
00), duplication can be avoided by starting Remote Terminal words from the
upper end, i.e., from 31 in all Systems except C120 Systems, where it is best
to start word settings backward from 15. Do not set words that are already
being used for other I/O points.
CPU Rack
IR 7
16 pts.
IR 5 & 6
32 pts.
IR 1, 2, 3, & 4
64 pts.
IR 0
16 pts.
Remote Terminal
IR 30
Section 3-2
Remote Terminal
IR 31
Set as terminator
31