CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
72
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FPGA-TN-02245-0.81
All rights reserved. CONFIDENTIAL
Clocks and Reset
MPCS Channel Clock Detail
This section describes the detailed implementation about the clock distribution inside MPCS channel. 8B/10B PCS
channel, 64B/66B PCS channel and PMA Only channel are discussed separately.
8B/10B PCS Clock
shows the 8B/10B PCS channel clock diagram.
8B/10B
Encoder
Tx User
Logic
(Fabric)
TX PMA
Tx FIFO
/2,
/1
tx_pcs_clk
TX Path
Tx Lane-to-Lane
Deskew
Word
Aligner
8B/10B
Decoder
Elastic
Buffer
RX PMA
Rx User
Logic
(Fabric)
Lane
Aligner
RX Path
Rx FIFO
/2,
/1
tx_lalign_clk
tx_pcs_clka
tx_pcs_clkb
tx_usr_clk
tx_out_clk
rx_usr_clk
rx_out_clk
rx_pcs_clkb
tx_lalign_clk
tx_pcs_clk
rx_pcs_clka
rx_lalign_clk
rx_pcs_clk
Figure 7.1. 8B/10B PCS Channel Clock Diagram
shows the detailed 8B/10B PCS Channel clock descriptions
.
Table 7.1. 8B/10B PCS Channel Clock
Clock
Direction
Description
PMA Interface (Hardened Connection)
tx_pcs_clk
N/A
This parallel data clock is generated by PMA Tx macro and used by MPCS to drive Tx
data bus. The source of this clock is Tx PLL.
rx_pcs_clk
N/A
This parallel data clock is generated by PMA Rx macro and used by MPCS to receive
data from Rx data bus. The source of this clock is the recovered clock from Rx CDR.
Fabric Interface
tx_out_clk
Output
This clock is directly connected to FPGA global buffer, and thus can drive FPGA clock
tree. In multiple-channel cases, channels may share the same clock tree with each
other. Therefore, not every tx_out_clk in channels is really used. The source of this
clock is selected by MPCS, depending on application cases.
This clock can be the divided-by-two version of its source clock.
rx_out_clk
Output
This clock is directly connected to FPGA global buffer and thus can drive FPGA clock
tree. In multiple-channel cases, channels may share the same clock tree with each
other. Therefore, not every rx_out_clk in channels is really used. The source of this
clock is selected by MPCS, depending on application cases.
This clock can be the divided-by-two version of its source clock.
tx_usr_clk
Input
This clock is a node of fabric clock tree. The data sent by user logic to MPCS is