2.1 Logic Levels

To determine whether a bit is 1 or 0, the receiving I/O performance is characterized by two parameters, Voltage Input High (VIH) and Voltage Input Low (VIL). VIH and VIL specify the worst-case inputs ensure to be 1 or 0. An input signal between these values is undefined behavior, as shown in Figure 2-1.

Figure 2-1. I/O Logic Versus Voltage
VIH and VIL ranges are specified in the data sheet of the device. Some devices may allow users to switch between fixed voltage thresholds or thresholds as a ratio of VDD.