SNLA415 August 2022 DS160PT801
A REFCLK, or reference clock signal, is a prerequisite for a PCIe device to begin data transmission. This 100 MHz reference clock signal is used by the PCIe device to generate the high-speed PCIe data within the link and is shared by the PCIe devices within the link. In Figure 4-1, it is referred as "REFCLK."