Why do 3.3V LVTTL/ LVCMOS input pins have the 3.3V LVTTL/ LVCMOS output IBIS model assigned to them for IBIS models generated by the Quartus® II software?

Description

The Quartus® II software will assign a 3.3V LVTTL/ LVCMOS output IBIS model for an input pin, if you have the PCI clamp diode enabled. The 3.3V LVTTL/ LVCMOS output IBIS model includes the 3.3V LVTTL/LVCMOS input buffer information.

For example, you may see the “ttl33_cio_d4ps3” output IBIS model assigned to the 3.3V LVTTL input pin with PCI clamp diode enabled.  You can simulate input functionality with this model.