Hi5a controllermaintenanceHi5a-S/P/C/T/J Controller Maintenance Manual4. Basic Components of Controller4.3. The Function of Each Component4.3.1. Rack and Backplane Board (BD502)On this page4.3.1. Rack and Backplane Board (BD502)4.3.1. Rack and Backplane Board (BD502) 4.3.1.1. Outline