Part Number : SN74HC257
Function : Quadruple 2-Line To 1-Line Data Selectors/Multiplexers With 3-State Outputs
Manufactures : Texas Instruments
These devices are designed to multiplex signals from 4-bit data sources to 4-output data lines in bus-organized systems. The 3-state outputs do not load the data lines when the output-enable (G\) input is at a high logic level.
To ensure the high-impedance state during power up or power down, (G\) should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.
Official Homepage : http://www.ti.com/product/sn74hc257
Block Diagram :