Description
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.

Features
• Buffered Inputs
• Typical Propagation Delay ( In to Output ) = 12ns at VCC = 5V, CL = 15pF, TA = 25°C
• Fanout (Over Temperature Range)
   - Standard Outputs . . . . . . . . . . . . . . . 10 LSTTL Loads
   - Bus Driver Outputs . . . . . . . . . . . . . 15 LSTTL Loads
• Wide Operating Temperature Range . . . -55°C to 125°C
• Balanced Propagation Delay and Transition Times
• Significant Power Reduction Compared to LSTTL Logic ICs
• HC Types
   - 2V to 6V Operation
   - High Noise Immunity: NIL = 30%, NIH = 30% of VCC at VCC = 5V
• HCT Types
   - 4.5V to 5.5V Operation
   - Direct LSTTL Input Logic Compatibility, VIL= 0.8V (Max), VIH = 2V (Min)
   - CMOS Input Compatibility, Il ≤ 1µA at VOL, VOH