About coupling
Although it depends on the specification of the Clock IC, select DC Coupling when using the HCSL standard.
In case of LVDS, AC coupling should be used.
The configuration diagram is also shown in the Clock IC Data Sheet. (Even in the case of HCSL standard, there are devices that require termination processing outside the Clock IC and devices that can be directly connected to the FPGA.)
About I/O Standard
Select the same I/O standard for the Tool according to the HCSL, LVDS, etc. standard you selected above.
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Category: PCI-Express
Tool: -
Device: Cyclone® V