74HCT138

The 74HC/HCT138 are high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A.

The 74HC/HCT138 decoders accept three binary weighted address inputs (A₀, A₁, A₂) and when enabled, provide 8 mutually exclusive active LOW outputs (Y₀ to Y₇).

The "138" features three enable inputs: two active LOW (E₁ and E₂) and one active HIGH (E₃). Every output will be HIGH unless E₁ and E₂ are LOW and E₃ is HIGH.

This multiple enable function allows easy parallel expansion of the "138" to a 1-of-32 (5 lines to 32 lines) decoder with just four "138" ICs and one inverter.

The "138" can be used as an eight output demultiplexer by using one of the active LOW enable inputs as the data input and the remaining enable inputs as strobes. Unused enable inputs must be permanently tied to their appropriate active HIGH or LOW state.

The "138" is identical to the "238" but has inverting outputs.