The Toshiba Strata XIIe and XXe 3-Port C.O. Interface PCB provides an interface between the HKSU and the central office or PBX lines. Ring detection, hold and dial outpulsing are performed by this PCB. Depending upon local CO requirements, each CO/PBX line can be programmed for DTMF or rotary dial outpulsing. Each HCOU PCB serves up to three CO/PBX lines.