3.6. Transmitter Data Path Interface Clocking
The clocks generated by the PLLs are used to clock the channel PMA and PCS blocks. The clocking architecture is different for the standard PCS and the enhanced PCS.
The master or the local CGB provides the high speed serial clock to the serializer of the transmitter PMA, and the low speed parallel clock to the transmitter PCS.
In the Standard PCS, for configurations that do not use the byte serializer, the parallel clock is used by all the blocks up to the read side of the TX phase compensation FIFO. For configurations that use the byte serializer block, the clock divided by 2 or 4 is used by the byte serializer and the read side of the TX phase compensation FIFO. The clock used to clock the read side of the TX phase compensation FIFO is also forwarded to the FPGA fabric to provide an interface between the FPGA fabric and the transceiver.
If the tx_clkout that is forwarded to the FPGA fabric is used to clock the write side of the phase compensation FIFO, then both sides of the FIFO have 0 ppm frequency difference because it is the same clock that is used.
If you use a different clock than the tx_clkout to clock the write side of the phase compensation FIFO, then you must ensure that the clock provided has a 0 ppm frequency difference with respect to the tx_clkout.
In the Enhanced PCS, the parallel clock is used by all the blocks up to the read side of the TX phase compensation FIFO. The clocks of all channels in bonded configuration are forwarded. You can pick tx_clkout as the source for clocking their TX logic in core.
For the enhanced PCS, the transmitter PCS forwards the following clocks to the FPGA fabric:
tx_clkout for each transmitter channel in non-bonded and bonded configuration. In bonded configuration, any tx_clkout can be used depending on your core timing requirements.
You can clock the transmitter datapath interface using one of the following methods:
- Quartus Prime selected transmitter datapath interface clock
- User-selected transmitter datapath interface clock
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