Data devices use the second I-channel of the DCP porotcol for local access. Three different data modules perform the conversion from RS-232 to DCP. The Digital Terminal Data Module (DTDM) is an adjunct ot the digital voice terminal. The Processor Data Module (PDM) interfaces RS-232 host ports to the PBX. The Trunk Data Module (TDM) provides the interface between DCP and modems.