CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
84
© 2020-2021 Lattice Semiconductor
FPGA-TN-02245-0.81
All rights reserved. CONFIDENTIAL
Rx
Gear Box
Block
Aligner
De-
Scrambler
64B/66B
Decoder
Rx
FIFO
Tx
FIFO
64B/66B
Encoder
Scrambler
Tx
Gear Box
16b data
TX Path
RX Path
PMA
/4
/4
BER
Monitor
66b block
2b sync
+ 64b data
8b TXC
+ 64b TXD
8b TXC
+ 64b TXD
16b data
66b block
2b sync
+ 64b data
2b sync
+ 64b data
8b RXC
+ 64b RXD
8b RXC
+ 64b RXD
tx_pcs_clk
(644.5MHz,
from Tx PLL)
tx_pcs_divclk (161.1328MHz)
tx_usr_clk
(156.25MHz)
tx_out_clk
(322.2656MHz)
rx_pcs_clk
(644.5MHz,
from Rx CDR)
rx_usr_clk
(156.25MHz)
rx_out_clk
rx_pcs_divclk (161.1328MHz)
rx_pcs_bufclk (322.2656MHz)
/2
tx_pcs_bufclk (322.2656MHz)
/2
Fabric
GPLL
64/66
Fabric
Figure 7.15. 64B/66B PCS with Using GPLL
64B/66B PCS
without GPLL
Case VI-a: Rx Path Clock Compensation is Enabled
shows an example of GPLL not being used. The tx_out_clk is used to drive both tx_usr_clk and rx_usr_clk
section for the Tx FIFO write timing diagram, and the
timing diagram. The Rx FIFO also works as CTC FIFO, to implements the functionality of clock tolerance compensation.
Rx
Gear Box
Block
Aligner
De-
Scrambler
64B/66B
Decoder
Rx
FIFO
Tx
FIFO
64B/66B
Encoder
Scrambler
Tx
Gear Box
16b data
TX Path
RX Path
PMA
/4
/4
BER
Monitor
66b block
2b sync
+ 64b data
8b TXC
+ 64b TXD
8b TXC
+ 64b TXD
16b data
66b block
2b sync
+ 64b data
2b sync
+ 64b data
8b RXC
+ 64b RXD
8b RXC
+ 64b RXD
tx_pcs_clk
(644.5MHz,
from Tx PLL)
tx_pcs_divclk (161.1328MHz)
tx_usr_clk
(161.1328MHz)
tx_out_clk
(161.1328MHz)
rx_pcs_clk
(644.5MHz,
from Rx CDR)
rx_usr_clk
(161.1328MHz)
rx_out_clk
rx_pcs_divclk (161.1328MHz)
rx_pcs_buffclk (322.2656MHz)
/2
tx_pcs_bufclk (322.2656MHz)
/2
Fabric
Fabric
DFF
DFF
Figure 7.16. 64B/66B PCS without using GPLL (Case I)
Case VI-b: Rx Path Clock Compensation is Disabled
shows an example of GPLL not being used and CTC functionality being disabled. The tx_out_clk is used to
drive tx_usr_clk, and rx_out_clk is used to drive rx_usr_clk respectively. Check
the
section for the Tx FIFO write
timing diagram, and the
section for the Rx FIFO read timing diagram. The clock tolerance compensation is
unnecessary, considering no clock frequency difference between rx_out_clk and rx_usr_clk.