This document introduces the features and parameters of the 74F157A / 74F158A data selectors / multiplexers. It is a high speed quad 2-input multiplexer which selects 4 bits of data from one of two sources under the control of a common select input (S). When E is high, all of the outputs (Yn) are forced low regardless of all other input conditions. Moving data from two registers to a common output bus is a common use of the 74F157A. The state of the select input determines the particular register from which the data comes. The device is the logic implementation of a 4-pole, 2-position switch where the position of the switch is determined by the logic levels supplied to the select input. The 74F158A is similar, but has inverting outputs (Yn).