Clocking - 1.0 English

• PCI Express® PHY IP GTH/GTY can be configured to support PCIe® applications with 100 MHz, 125 MHz, or 250 MHz reference clock.
• The reference clock can be synchronous or asynchronous.
• The phy_pclk is the primary clock for the PIPE interface, FPGA fabric, and GTH/GTY [TX/ RX] usrclk and [TX/RX] usrclk2.
• In addition to phy_pclk, two other clocks (phy_coreclk and phy_userclk ) are available to support the PCIe MAC
• BUFG_GTs are used to generate these clocks, so MMCM will not be required.
• The source of the GTH/GTY reference clock must come directly from IBUFDS_GTE4 for UltraScale+ devices and from IBUDS_GTE3 for UltraScale devices.
• To use the reference clock for FPGA fabric, another BUFG_GT must be used.
• The gt_gtpowergood output port of the PCIe PHY IP must drive the CE pin of BUFG_GT.

The following figure shows an x2 PCIe architecture example.

For more information on PHY IP Clocking, refer to the Clocking section in the UltraScale+ Devices Integrated Block for PCI Express LogiCORE IP Product Guide (PG213).