The Allen-Bradley 1747-BSN is a backup scanner module. The 1747-BSN backup scanner is available with redundancy for remote I/O (RIO). The 1747-BSN is equipped with RS-232 channel switching for communication with devices such as operator interfaces. This module also has a DH+ link. This module is a set of complementary modules, with one module located in the main system and other modules in the secondary or backup system. The main module controls all the remote I/O operations.