What IO standards should I choose for PCIE signals?

[Altera_Forum]

Hello: 

 I am using cyclone IV GX,  Should I choose 1.5v PCML for PCI-E data out and PCI-E data in? Should I choose HCSL for PCI-E reference clock in?  I can't find any documents about IO standard for PCI-E signals.   Thank you.

[Altera_Forum]

Yes. 

 If in doubt refer to an example project from Altera. You can find these included with development kits.  E.g. cyclone iv gx transceiver starter kit (http://www.altera.com/products/devkits/altera/kit-cyclone-iv-starter.html). Download the kit installation and explore.  Cheers, Alex

[Altera_Forum]

This is what I have for a design in the Stratix V, works fine for me (@Gen 1, 2 and 3): 

  set_instance_assignment -name IO_STANDARD HCSL -to pcie_refclk set_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to pcie_perstn set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_0 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_1 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_2 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_3 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_4 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_5 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_6 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_rx_7 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_0 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_1 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_2 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_3 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_4 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_5 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_6 set_instance_assignment -name IO_STANDARD "1.5-V PCML" -to pcie_transciever_tx_7

[Altera_Forum]

Hi ridgemao, 

 For the refclk IO standard information, you could refer to Table 1–6. REFCLK I/O Standard Support in the Cyclone IV Device Handbook, Volume 2. There it is stated that you could use HCSL for PCIe refclk with DC coupling. If you are using AC coupling, then you can choose from LVDS, LVPECL and PCML.  As for the CIV TX, it only support 1.5V PCML. CIV RX can take LVDS, LVPECL and PCML.