Bus-holder

A bus-holder or bus-keeper is a weak latch circuit that holds the last value on a tri-state bus.

The circuit is basically a delay element with the output connected back to the input through a relatively high impedance.

Bus-holders are used to prevent CMOS gate inputs from getting floating values when they are connected to tri-stated nets.

In severe cases, this increased power consumption can destroy the CMOS gate.

This is prevented by the bus-holder pulling the input to the last valid logic level (0 or 1) on the net.