1.2.4. Transmitter PLLs
Each transmitter channel has a clock divider called a local clock divider. The clock dividers generate the parallel and serial clock sources for the transmitter and optionally for the receiver PCS. The clock dividers on channels 1 and 4 are called central clock dividers because they can drive the x6 and xN clock lines. The central clock dividers can feed the clock lines used to bond channels.
The high-speed serial clock and low-speed parallel clock skew between channels and unequal latency in the transmitter phase compensation FIFO contribute to transmitter channel-to-channel skew. In bonded channel configurations the parallel clock is generated by a central clock divider for all channels, rather than using a local clock divider for each transmitter channel. Also, the transmitter phase compensation FIFO in all bonded channels shares common pointers and control logic generated in the central clock divider, resulting in equal latency in the transmitter phase compensation FIFO of all bonded channels. The lower transceiver clock skew and equal latency in the transmitter phase compensation FIFOs in all channels provide lower channel-to-channel skew in bonded channel configurations.
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