Bus Holder / Keeper Latch / Autolatch

This circuit keeps the input of the inverter U1 at a valid logic state even when the input signal IN gets disconnected (by opening the switch). Inverter U2 creates positive feedback, the feedback resistor limits the current when the input signal and the output of inverter U2 are in opposing logic state. When the switch is opened the feedback inverter pulls the input of inverter U1 to a valid logic state. Hence, the input does not float. The presence of feedback resistor allows the input signal IN to be applied even when the feedback inverter is also driving the same line. This circuit is called Bus Holder by TEXAS INSTRUMENTS, Keeper Latch by LATTICE SEMICONDUCTOR, and Autolatch by ZiLOG. Some other semiconductor device manufacturers call it by other names.