FSTU3257 is a Fairchild high-speed CMOS TTL-compatible 4:1 multiplexer/demultiplexer bus switch, low on resistance allows inputs to be connected to outputs without adding propagation delay or generating additional ground bounce noise. When OE is low, the select pin connects the A port to the selected B port output. The A and B ports are "undershoot hardened" with Undershoot Hardened Circuit (UHC®) protection to support an extended range of 2.0V below ground. Fairchild's integrated UHC senses undershoot at the I/O and responds by preventing voltage differentials from developing and turning on the switch. When OE is high, the switch is open and a high-impedance state exists between the two ports.