The CY74FCT2257T 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 appears at the output in noninverted form for the CY74FCT2257T. On-chip
termination resistors at the outputs reduce system noise caused by reflections. The CY74FCT2257T can
replace the FCT257T to reduce noise in an existing design.
The CY74FCT2257T is a logic implementation of a four-pole, two-position switch, in which the position of the
switch is determined by the logic levels supplied to S. Outputs are forced to the high-impedance off state when
the output-enable (OE\) input is high.
All but one device must be in the high-impedance state to prevent currents from exceeding the maximum ratings
if outputs are tied together. Design of the OE\ signals must ensure that there is no overlap when outputs of 3-state
devices are tied together.
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.
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