The Global Clock (GC) pins are clock input pins; however, they can also be used as clock output. In G35D, these pins are configured as general-purpose I/Os, so the GC pins can either be used as an input or output clock.
The G35D devkit’s FMC HPC connector provides support for 2 Clock-Input-Capable LVDS/SE pins from the HP bank and 1 Clock-Output-Capable LVDS/SE pin from the HP bank which are directly connected to the SoC. These pins can be configured as GC (Global Clock) input /output or differential/single-ended I/O, depending on the requirements. No buffers or hardware clock are used for these GC clock pins.
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Please find the detailed G35D product information in the below link,