The M54/74HCT257 and the M54/74HCT258 are high speed CMOS MULTIPLEXERs fabricated with silicon gate C2MOS technology. They have the same high speed performance of LSTTL combined with true CMOS low power consumption. These IC's are composed of an independent 2channel multiplexer with common SELECT and ENABLE INPUT. The M54/74HCT258 is an inverting multiplexer while the M54/74HCT257 is a non-inverting multiplexer. When the ENABLE INPUT is held "High", outputs of both IC's become high-impedance state. If SELECT INPUT is held "Low", "A" data is selected, when SELECT INPUT is high "H", "B" data is chosen.