The CY74FCT257T has four identical two-input multiplexers that select four bits of data from two sources under
the control of a common data-select (S) input. The I0 inputs are selected when S is low, and the I1 inputs are
selected when S is high. Data at the output is noninverted.
The CY74FCT257T is a logic implementation of a four-pole, two-position switch, where the position of the switch
is determined by the logic levels at S. Outputs are in the high-impedance state when the output-enable (OE\)
input is high.
All but one device must be in the high-impedance state to avoid currents exceeding the maximum ratings if
outputs are tied together. OE\ inputs must ensure that there is no overlap when outputs of 3-state devices are
This device is fully specified for partial-power-down applications using Ioff. The Ioff circuitry disables the outputs,
preventing damaging current backflow through the device when it is powered down.