CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
FPGA-TN-02245-0.81
© 2020-2021 Lattice Semiconductor
83
All rights reserved. CONFIDENTIAL
Word
Aligner
8B/10B
Decoder
Elastic Buffer
Rx
PMA
Lane
Aligner
Channel 0 RX Path
Rx FIFO
/2,
/1
Clock
Tree
DFF
Fabric
Quad
Common
Word
Aligner
8B/10B
Deco der
Elastic Buffer
Rx
PMA
Lane
Aligner
Rx FIFO
/2,
/1
DFF
Fabric
Channel 1 RX Path
rx_pcs_clk0
rx_lalign_clk
rx_pcs_clka0
tx_pcs_clk0
tx_lalign_clk
rx_pcs_clkb0
rx_out_clk0
rx_pcs_clk1
rx_lalign_clk
rx_pcs_clka1
tx_pcs_clk1
tx_lalign_clk
rx_pcs_clkb1
rx_out_clk1
Figure 7.14. Case IV-b Clock Structure
64B/66B PCS
with GPLL
Case V-a: 64B/66B PCS with GPLL
the tx_pcs_clk is generated clock from PMA Tx PLL, and the rx_pcs_clk is recovered clock from
PMA Rx CDR. The source of tx_out_clk and rx_out_clk can be divided-by-two version or divided-by-four of tx_pcs_clk
and rx_pcs_clk respectively.
A General PLL (GPLL) is recommended to be used in fabric to generate the 156.25 MHz clock to drive both Tx XGMII
data path and Rx XGMII data path.
All modules inside 64B/66B PCS channel are recommended to be enabled, considering this 64B/66B PCS being designed
for Ethernet 10GBASE-R only. However, certain module can be disabled or bypassed only for test purposes.
shows an example of all modules being enabled. The tx_out_clk is used to drive GPLL to generate
156.25MHz tx_usr_clk and rx_usr_clk. Tx FIFO is enabled to eliminate the clock frequency difference between
tx_pcs_divclk and tx_usr_clk. Rx FIFO is enabled to eliminate the clock frequency difference between rx_pcs_divclk and
rx_usr_clk. Check
section for the Tx FIFO write timing diagram, and the
timing diagram.
The Rx FIFO also works as CTC FIFO, to implements the clock tolerance compensation required by Ethernet 10GBASE-R
protocol.