CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
FPGA-TN-02245-0.81
© 2020-2021 Lattice Semiconductor
127
All rights reserved. CONFIDENTIAL
Table A. 15. Tx Amplitude Ratio [reg18]
Field
Name
Access
Width
Reset
Description
[7:0]
tx_amp_ratio
RW
8
8’h80
This register implements the Tx amplitude ratio used by
the Tx driver. A value of 128 corresponds to 100% (full
voltage) whereas a value of 0 corresponds to 0%. Value
higher than 128 are forbidden. This register is used in PCIe
Gen1/Gen2/Gen3 and non-PCIe mode.
Table A. 16. CDR PLL Frequency Comparator Maximum Difference [reg21]
Field
Name
Access
Width
Reset
Description
[7:0]
cdrpll_cmp_max
RW
8
8’h14
This register defines the threshold after which the
frequency comparator considers that the TxClk and RxClk
are too much difference in order to consider that the CDR
PLL has lost lock and thus decide to relock the CDR PLL in
frequency mode.
PPM_threshold = (reg21 – 2) * reg22 (ppm).
Example: reg21 = 8’h8, and reg22 = 8’h4, then
PPM_threshold = (8 – 2) * (4 * 256) (ppm) = 6144(ppm).
Table A. 17. CDR PLL Frequency Comparator Counter [reg22]
Field
Name
Access
Width
Reset
Description
[7:0]
cdrpll_cnt_max
RW
8
8’h4
This register defines the number of 256 clock cycles for
evaluating the frequency difference between TxClk and
RxClk.
Table A. 18. EI4 Mode Register [reg23]
Field
Name
Access
Width
Reset
Description
[7]
EI4
RW
1
1’b0
Electrical Idle selection.
1’b1 – EI4 instead of EI1.
1’b0 – EI1.
[6:3]
reserved
RSVD
4
4’b0000
—
[2]
rstcdr_idl
RW
1
1’b0
Reset CDR whenever Electrical Idle is detected on Rx
(LOS).
1’b1 – the CDR is put into reset each time that Electrical
Idle is detected on Rx (Loss of Signal). This bit must not
be set in protocol where EI is actively used and requires
short exit time (PCIe and USB3).
1’b0 – do not reset CDR.
[1]
rstcdr_frq
RW
1
1’b1
Reset CDR whenever frequency comparator trigger an
error, and direct back the CDR to frequency lock mode
(LOL).
1’b1 – reset.
1’b0 – do not reset.
[0]
rstcdr_err
RW
1
1’b1
Reset CDR whenever the error gathering function reports
an error and direct back the CDR to frequency lock mode
(LOL).
1’b1 – reset.
1’b0 – do not reset.
Table A. 19. PMA Controller Status [reg30]
Field
Name
Access
Width
Reset
Description
[7]
pma_rdy
RO
1
NA
Defines whether PMA has completed its internal