CertusPro-NX SerDes/PCS Usage Guide
Preliminary
Technical Note
48
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FPGA-TN-02245-0.81
All rights reserved. CONFIDENTIAL
The SerDes includes an eye monitor to map the post-equalized eye density. Eye X and Y coordinates can be controlled,
and the error density can be calculated at each coordinate. The X coordinate can be set by a 6-bit bus in 1.5mVdiff
(minimum) increments with a separate sign bit, and the Y coordinate by a 6-bit bus in UI/64 increments.
The PLL Clock blocks generate the required Tx and Rx link clocks and high frequency internal clocks from the provided
reference clock source, and contain all the control-feedback loops. Multiple single-lane macros may be formed into
wider transmit and/or receive links with support from the PCS as required by the relevant standards.
AC Coupling
For most serial protocols, each PMA channel needs to be AC coupled externally. Suitable values for AC coupling
capacitors have to be used to maximize link signal quality, and conform to respective standards specifications.
Take PCI Express as example, the AC coupling capacitors should be placed near Tx side (
Figure 6.2. PCI Express AC Coupling Capacitors Location
PLL Clock Setting
Tx and Rx rates can be different frequencies, but limited to certain allowed integer ratios. The architecture of Tx PLL
and CDR PLL is similar. You can configure PLL VCO frequency F
VCO
, PMA internal clock frequency F
bit
, and PMA parallel
output clock frequency F
PMA
by accessing related PMA registers.
Following equation shows the relationship between F
VCO
, F
bit
, F
PMA
, and PMA reference clock frequency F
Ref
. For detailed
PLL setting for specific protocols, refer to the
section. M can be set as 1, 2, 4, and 8; F can be set as 1,
2, 3, 4, 5, and 6; N can be set as 5, 8, 10, 16, and 20.
𝐹
𝑉𝐶𝑂
= 𝐹
𝑅𝑒𝑓
× 𝑀 × 𝑁 × 𝐹
𝐹
𝑏𝑖𝑡
= 𝐹
𝑉𝐶𝑂
/𝑀 = 𝐹
𝑅𝑒𝑓
× 𝑁 × 𝐹
𝐹
𝑃𝑀𝐴
= 𝐹
𝑏𝑖𝑡
/𝑁 = 𝐹
𝑅𝑒𝑓
× 𝐹
shows the operation range for PMA reference clock frequency F
Ref
, PLL VCO frequency F
VCO
, PMA internal
clock frequency F
bit
, and PMA parallel output clock frequency F
PMA
.
Table 6.1. Operation Range for F
Ref
, F
VCO
, F
bit
, and F
PMA
Minimum (MHz)
Maximum (MHz)
PMA reference clock frequency F
Ref
74.25
162
PLL VCO frequency F
VCO
5000
10312.5
PMA internal clock frequency F
bit
625
10312.5
PMA parallel output clock frequency F
PMA
—
500 (644.53 for 64B/66B PCS only)