The A and B Ports are protected against undershoot to support an extended range to 2.0V below ground. Fairchild's integrated Undershoot Hardened Circuit (UHC) senses undershoot at the I/O, and responds by preventing voltage differentials from developing and turning the switch on. Another innovative device feature is the addition of a level shifting select pin, "S2 and S5". When S2 and S5 are LOW, the device behaves as a standard N-MOS switch. When S2 and S5 are HIGH, a diode to VCC is integrated into the circuit allowing for level shifting between 5V inputs and 3.3V outputs.