What is the advantage of using index registers?

The most beneficial use of index registers is to reduce the number of steps required in ladder programming.

When processing a continuous or uniformly spaced list of addresses in a ladder program, the exact same programming pattern may appear 10 to 20, or even hundreds of times. This can be true for sequence control (bit processing) and data processing (word processing) as well. In these situations, the number of steps used in a ladder program can be greatly reduced by using an index register in a FOR-NEXT loop.

The CVM1, CV500/CV1000/CV2000, and CS1/CJ1 Programmable Controllers' support index registers.