Hi5a controllermaintenanceHi5a Controller Maintenance Manual4. Basic Components of Controller4.3. The Function of Each Component4.3.1. Rackand Backplane Board (BD502)On this page4.3.1. Rackand Backplane Board (BD502)4.3.1. Rackand Backplane Board (BD502) 4.3.1.1. Outline