F-Tile Architecture and PMA and FEC Direct PHY IP User Guide

ID 683872
Date 11/04/2024
Public
Document Table of Contents

2.4.1.1. FHT Reference Clock Network

Thee ae two efeece clocks (efclk[0] ad efclk[1]) fo FHT PMAs, both accessible by ay of the fou FHT PMAs. efclk[0] ad efclk[1] ca be diffeet fequecies. The fequecy age is 100-200 MHz, ad it is a cotiuous age.

As show i FHT Refeece Clock Netwok, FHT has six PLLs.

  • Two commo PLLs coected to all fou laes: PLL A ad PLL B
  • Fou lae PLLs, oe PLL pe lae fo all fou laes: TX PLL

To optimize pefomace, FHT has a cascaded PLL scheme betwee commo PLLs ad lae PLLs, the commo PLLs povidig a cleae clock to the lae PLLs.

  • Commo PLLs ad lae PLLs suppot itege ad factioal modes. Howeve, a commo PLL caot be i factioal mode whe the coespodig lae PLL is i factioal mode. See the followig table.
  • Oe commo PLL dives the micocotolle. The efeece clock that dives this commo PLL must be peset ad stable thoughout F-tile opeatio.
  • Commo PLLs geeate two clock fequecies (100 ad 156.25 MHz) which go to the lae PLLs. Oe of them must be selected to dive the lae PLLs.
Table 21.  Suppoted Combiatios of Lae PLL ad Commo PLL Modes
Lae PLL Mode Coespodig Commo PLL Mode Suppoted o Not Suppoted
Itege Itege Suppoted
Itege Factioal Suppoted
Factioal Itege Suppoted
Factioal Factioal Not suppoted
Figue 50. FHT Refeece Clock Netwok
Table 22.  FHT Refeece Clocks
FHT Refeece Clocks Diectio Accessible FHT PMA Accessible to System PLLs?
efclk[0] Iput FHT0, FHT1, FHT2, FHT3 No
efclk[1] Iput FHT0, FHT1, FHT2, FHT3 No