CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
FPGA-TN-02245-0.81
© 2020-2021 Lattice Semiconductor
75
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PMA Only Mode Clock
shows the PMA Only mode clock diagram.
shows the PMA Only mode channel clock detailed
descriptions.
Tx User
Logic
(Fabric)
TX
PMA
Tx FIFO
/2,
/1
RX
PMA
Rx User
Logic
(Fabric)
tx_pcs_clk
TX Path
RX Path
Tx Lan e-to-lane
Deskew
Rx FIFO
/2,
/1
tx_lalign_clk
tx_pcs_clka
tx_pcs_clkb
tx_out_clk
tx_usr_clk
rx_usr_clk
rx_out_clk
rx_pcs_clk
Figure 7.3. PMA Only Mode Clock Diagram
Table 7.3. PMA Only Mode 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
synchronous to this clock.
rx_usr_clk
Input
This clock is a node of fabric clock tree. The data received by user logic from MPCS is
synchronous to this clock.
Channel Internal Clock
tx_pcs_clka
N/A
This clock drives most part of Tx path logics. It may come from tx_pcs_clk in single-
channel application or from tx_lalign_clk in multiple-channel application where all
channels need to be aligned.
tx_pcs_clkb
N/A
This clock has the same frequency as tx_pcs_clka or half frequency of tx_pcs_clka,
depending on input data rate and bus width. This clock and tx_pcs_clka are positive
edge aligned, with as little skew as possible between them so that output data from
this clock domain can be sampled by tx_pcs_clka directly.