The MC74HC257 is identical in pinout to the LS257. The device inputs are compatible with standard CMOS outputs; with pullup resistors, they are compatible with LSTTL outputs. This device selects a (4bit) nibble from either the A or B inputs as determined by the Select input. The nibble is presented at the outputs in noninverted form when the Output Enable pin is at a low level. A high level on the Output Enable pin switches the outputs into the highimpedance state. The HC257 is similar in function to the HC157 which do not have 3state outputs.