DESCRIPTION AND APPLICATION
   The VCT1000B is a hitless-switching dual-input stratum 3 low jitter timing module with status outputs and alarms. Dual 8 kHz references are independently selected to lock a digital phase lock loop resulting in excellent long and short-term stability. Two control inputs are used to steer the state machine decisions for the operation of the module. The state machine will enter and maintain the operation in the free run, holdover, or locked condition. The state machine operates under the requirements of section 3.4 of the Telcordia GR-1244-CORE. Four status pins indicate the condition, which the unit is operating, and two alarm outputs indicate the loss of lock and holdover or free run operation. The signal outputs are the low jitter oscillator output and the divided 8kHz output. Input phase rearrangement allows the output to remain hitless upon the switching of the references, regardless of input phase. Dimensions are 2” x 2” x 0.55”. A state machine is used to assure that switching to a bad reference is not allowed, and that both references are qualified.