DESCRIPTION
The LS157 is a Quad 2-Input Multiplexer fabricated with the Schottky barrier diode process for high speed. It selects four bits of data from two sources under the control of a common Select Input (S). The Enable Input (E) is active LOW. When E is HIGH, all of the outputs (Z) are forced LOW regardless of all other inputs. The LS157 is the logic implementation of a 4-pole, 2-position switch where the position of the switch is determined by the logic levels supplied to the Select Input. The logic equations for the outputs are: Za = E ⋅ (I1a ⋅ S + I0a ⋅ S) Zc = E ⋅ (I1c ⋅ S + I0c ⋅ S) Zb = E ⋅ (I1b ⋅ S + I0b ⋅ S) Zd = E ⋅ (I1d ⋅ S + I0d ⋅ S) A common use of the LS157 is the moving of data from two groups of registers to four common output busses. The particular register from which the data comes is determined by the state of the Select Input. A less obvious use is as a function generator. The LS157 can generate any four of the 16 different functions of two variables with one variable common.
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