NT5D97 Dual-port DTI2/PRI2 card Page 353 of 906Circuit Card Description and InstallationArchitectureClock operationThere are two types of clock operation - tracking mode and free-run mode.Tracking modeIn tracking mode, the DDP2 loop supplies an external clock reference to aclock controller. Two DDP2 loops can operate in tracking mode, with onedefined as the primary reference source for clock synchronization, the otherdefined as the secondary reference source. The secondary reference acts as aback-up to the primary reference.As shown in Figure 77, a system with dual CPUs can have two clockcontrollers (CC-0 and CC-1). One clock controller acts as a back-up to theother. The clock controllers should be completely locked to the referenceclock.Free run (non-tracking) modeThe clock synchronization of the can operate in free-run mode if:• no loop is defined as the primary or secondary clock reference,• the primary and secondary references are disabled, or• the primary and secondary references are in local (near end) alarm13 ON OFF ON ON14 OFF ON ON ON15 ON ON ON ONTable 138Switch setting for MSDL external card (Part 2 of 2)Switch SettingDNUM (LD 17) 1 2 3 4
