19.7 INLVLx - Input Threshold Control

The INLVLx register controls the input voltage threshold for each available PORTx input pin. A selection between the Schmitt Trigger (ST, CMOS-compatible) and the Low-Voltage Buffer (LVBUF, TTL-compatible) thresholds is available.

The ST input buffer provides voltage-dependent input sensing, meaning the V_IL and V_IH levels are proportional to the supply voltage (V_DD). The ST buffer typically has a wide gap between V_IL and V_IH levels (hysteresis). The ST buffer is also compatible with CMOS levels.

Unlike the ST buffer, the LVBUF input buffer provides voltage-independent input sensing, meaning the V_IL and V_IH levels remain constant for the entire range of supply voltage (V_DD). The LVBUF buffer typically has very low V_IL and V_IH levels with a smaller hysteresis, thus making it an ideal choice for low-voltage input irrespective of the V_DD supply voltage. The LVBUF buffer is also compatible with TTL levels.

Choosing an appropriate input threshold is vital in determining the value of a read of the PORTx register and the level at which an interrupt-on-change occurs if that feature is enabled. Refer to the I/O Ports table in the "Electrical Specifications" chapter for more details on the threshold levels.

Important: Changing the input threshold selection must be performed while all peripheral modules are disabled. Changing the threshold level during the time a module is active may inadvertently generate a transition associated with an input pin, regardless of the actual voltage level on that pin.