74HCT158

The 74HCT158 is high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC tandard no. 7A.

The 74HCT158 is quad 2-input multiplexers which elect 4 bits of data from two sources and are controlled by common data select input (S). The four outputs present he selected data in the inverted form. The enable input (E) s active LOW.

When E is HIGH, all the outputs (1Y to 4Y) of the 74HCT158 are forced IGH regardless of all other input conditions.

Moving the data of the 74HCT158 from two groups of registers to four ommon output buses is a common use of the "158". The tate of S determines the particular register from which the ata comes. It can also be used as a function generator.

The 74HCT158 is useful for implementing highly irregular logic y generating any four of the 16 different functions of two ariables with one variable common.

The "158" is the logic implementation of a 4-pole, -position switch, where the position of the switch is etermined by the logic levels applied to S.

The logic equations of the 74HCT158 for the output are:
1Y = E.(1l₁.S + 1l₀.S)
2Y = E.(2l₁.S + 2l₀.S)
3Y = E.(3l₁.S + 3l₀.S)
4Y = E.(4l₁.S + 4l₀.S)
The "158" is identical to the "157" but has inverting outputs.