Solution:

There are two cases where an IO pad is driven by an external source. One is the case of a dedicated input pad, and the other is a bi-directional IO pad in which its output can be tri-stated. The "Dedicated Input Voltage Applied" and "I/O Tristate Voltage Applied" ranges specified under the Absolute Maximum Ratings section in MachXO data sheet cover these two cases, respectively. Any voltage stress driven from the external source above these ranges may cause permanent damage to the device.

Note that these absolute maximum rating values are not for the normal functional operations. These parameters also have an allowance of -2V to VIHMAX+2V that is only during the instantaneous overshoot and undershoot. The MachXO devices accept this allowance range only for the period of 20ns or shorter. For example, if you have a 3.3V input signal with 15ns overshoot pulses measured at 4.0V, this input signal level is allowed because:

1. The 3.3V input is within the absolute maximum rating (-0.5V to 3.75V)
2. The 4.0V level during overshoot is also allowed because the overshoot period is shorter than 20ns.