The 2500C-RADP-RS485 is a Compact RS485 RBC Adapter which allows a Series500 I/O base to function as a slave node on an RS485 Remote I/O channel. It provides a transparent path for upgrading old Series 500 systems without the requirement to completely replace the system.  Failed 500 Series RBCs can be replaced with CTI 2500 Series® Compact equivalents. Then, when your budget allows, you can plan a complete replacement of your system to CTI 2500 Series® - without losing your investment in the replaced modules!