Why do I receive a "Can't place input pin" or "Cannot place I/O" compilation error after applying my GXB pin location assignments when no ALTGXB megafunction exists in my design?

You may see the following compilation errors in the Quartus® II software, if you make pin assignments to your dedicated GXB pins without instantiating and fully connecting the ALTGXB megafunction in your design:

For inputs:
Error: Can't place input pin <pin name> in <pin location> because the pin is not connected to GXB Transceiver logic but the location is GXB Receiver pin.

For outputs:
Error: Cannot place I/O <pin name> in <pin location> because the I/O is not connected to GXB transmitter.

To avoid these errors, follow these steps: 

1. Instantiate the ALTGXB megafunction in your design.
2. Ensure that all megafunction ports are fully connected.
3. Apply the Virtual Pin assignment to any internal or core-side signals that should not connect to device I/O pins.