AR# 43641

描述

Typically, PCI reference clocks are sourced with a HCSL I/O standard.

Does GTP/GTX/GTH/GTY support REFCLKs with a HSCL I/O standard?

解决方案

GTP/GTX/GTH/GTY generally supports REFCLKs from LVDS/LVPECL oscillators as mentioned in the user guide. 

When there is a requirement to source HCSL I/O standards (as required by PCI applications), the HSCL clock will work with the 7 series and UltraScale/UltraScale+ GTs as long as they meet the phase noise mask requirement, the voltage swing, and any other requirements laid out in the datasheet. 

HCSL normally does meet these requirements and can be used. 

7 Series Phase noise masks can be found in (Xilinx Answer 44549). The UltraScale phase noise masks can be found in the device data sheets.

To reach the proper and expected voltage swing requires the proper topology. 

In the diagram below, if Rs is 33 ohm and internal to the chip is the 50 ohm Rt, the swing will be in the range of 750mv X2 or 1550mv diff.

The user must make sure their network will deliver the required voltage swing.