View mc74hc251 datasheet:

MOTOROLA SEMICONDUCTOR TECHNICAL DATA MC54/74HC251 8-Input Data Selector/ Multiplexer with J SUFFIX 3-State Outputs CERAMIC PACKAGE 16 High–Performance Silicon–Gate CMOS CASE 620–10 1 The MC54/74HC251 is identical in pinout to the LS251. The device inputs are compatible with standard CMOS outputs; with pullup resistors, they are N SUFFIX compatible with LSTTL outputs. PLASTIC PACKAGE This device selects one of the eight binary Data Inputs, as determined by 16 CASE 648–08 the Address Inputs. The Output Enable pin must be a low level for the 1 selected data to appear at the outputs. If Output Enable is high, both the Y and the Y outputs are in the high–impedance state. This 3–state feature D SUFFIX allows the HC251 to be used in bus–oriented systems. 16 SOIC PACKAGE