For a single-ended pin too close to a differential pin, Quartus® II software versions 3.0 and higher will produce this error:
Error: Non-differential I/O pin [pin name] in pin location [pin location] and pad [pad location] too close to differential I/O pin [pin name] in pin location [pin location] and pad [pad location] ...Cause = You assigned the specified I/O pin with a non-differential assignment to the specified pin location in the device that is too close to a differential pin in the specified location.
Action = Assign the I/O pin to a different location.
If the problem pin has a very low toggle rate (e.g. reset pin), you can apply an I/O Maximum Toggle Rate assignment of 0MHz on that single-ended pin to bypass this error message. For more information on this logic option, refer to the Quartus II Help file.
It is not advisable to apply a toggle rate logic option of 0MHz to any actively switching pin. The pin placement rules in the Quartus II software are enforced to ensure that noisy signals do not corrupt neighboring signals. If you choose to use the toggle rate logic option on switching pins in order to bypass these placement rules, your design may not function as intended.