The HC257 and HCT257 are quad 2-input multiplexers
which select four bits of data from two sources under the control of a common Select Input (S). The Output Enable
input (OE\) is active LOW. When OE\ is HIGH, all of the outputs
(1Y-4Y) are in the high impedance state regardless of
all other input conditions.
Moving data from two groups of registers to four common
output buses is a common use of the 257. The state of the
Select input determines the particular register from which
the data comes. It can also be used as a function generator.
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