CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
FPGA-TN-02245-0.81
© 2020-2021 Lattice Semiconductor
125
All rights reserved. CONFIDENTIAL
Table A. 9. Rx PLL M & N Settings [reg07]
Field
Name
Access
Width
Reset
Description
[7]
reserved
RSVD
1
1’b0
—
[6:5]
RxM
RW
2
2’b10
Defines the CDRPLL M setting.
2’b11 – 8
2’b10 – 4
2’b01 – 2
2’b00 – 1
[4:0]
RxN
RW
5
5’h04
Defines the CDR PLL N setting.
5’b10011 – 20
5’b01111 – 16
5’h01001 – 10
5’b00111 – 8
5’b00100 – 5
Note: This register can be reprogrammed when the PHY is under reset or both CDR PLL and Tx PLL are under reset.
Table A. 10. 250ns Timer Base Count [reg08]
Field
Name
Access
Width
Reset
Description
[7:0]
cnt250ns_max
RW
8
8’h7C
This register defines the base count of a 250ns event
based on Tx CLK (Frequency is F
PMA
) clock. This counter is
used by the CDR PLL and PMA Controller for operation
such as receiver detect, Electrical Idle.
In case of non-integer value, the base count should be
rounded up. Note that this register must be set correctly
for all protocols.
This register aims to generate an internal timing event
every 250ns or more internally for PMA Controller to
calibrate, CDR PLL lock to reference clock and data,
receive detect operation.
For example, for PCIe Gen1/Gen2/Gen3, Tx CLK is
500MHz. So that the value of this register should be 8’h7C
((124 + 1) * 2ns = 250ns).
Note: This register can be reprogrammed when the PHY is under reset.
Table A. 11. Tx Impedance Ratio [reg09]
Field
Name
Access
Width
Reset
Description
[7:0]
tx_imped_ratio
RW
8
8’h80
Tunes the Tx impedance ratio of the PMA.
8’h80 – 100 Ω
8’h55 – 150 Ω corresponds to 2/3 ratio
Note: This register can be reprogrammed when the PHY is under reset or when calibration has completed (PMA is ready).
Table A. 12. Tx Post-Cursor Ratio [reg0a]
Field
Name
Access
Width
Reset
Description
[7:0]
tx_pst_ratio
RW
8
8’h15
This register defines the Tx post-cursor ratio for PCI Gen1
speed or non-PCIe protocols. A value of 8’d128
corresponds to 100% (full voltage) whereas a value of 8’d0
corresponds to 0%.
Note: This register can be reprogrammed during normal operation, but effect only appears when the parameter for SerDes (PMA)
transmitter has been updated (at the end of calibration, on entry or exit of Tx electrical idle or when reg80 bit 1 has been
programmed).