2.2.1. Clock Tree
The unit support has a Synchronous logic which consists of Network Interface Synchronizer
chip, Jitter attenuators and clock buffers. The key component is a Network Interface Synchronizer
chip.
The Network Interface Synchronizer chip selects a reference clock from one of two valid clock
sources generating a Stratum 3 compliant reference clock for the Broadcom Trident chip. This clock
is also used as a transmit reference clock for all external interface ports. This logic consists of a IDT
89307 Network Interface Synchronizer chip and Oven controlled crystal oscillator. This synchronizer
chip when properly configured will produce 25MHz and 156.25MHz clock which is frequency locked
to a selected port recovered clock.
The IDT 89307 is configured through an I2C interface, it reports major state information via a
number of status and control signals.
Figure 3 Switch board clock Tree
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