74HC138 / 74LS138 3-to-8 Line Decoder IC – High-Speed Demultiplexer DIP-16

Overview

The 74HC138 (High-speed CMOS) and 74LS138 (Low-power Schottky) are high-performance decoders/demultiplexers. They take a 3-bit binary input ($A_0, A_1, A_2$) and activate one of the eight active-low outputs ($Y_0$ to $Y_7$). These ICs are essential for “Address Decoding” in computer memory systems or for controlling multiple devices using only 3 pins from your microcontroller.

Key Features

• 3-to-8 Line Decoding: Convert 3 binary inputs into 8 unique outputs.

• Demultiplexing Capability: Can be used as a 1-to-8 demultiplexer by using the Enable pins as data inputs.

• Multiple Enable Inputs: Features three Enable pins ($E_1, E_2, E_3$) for easy “cascading” (linking multiple chips to control 16, 24, or 32 outputs).

• Active-Low Outputs: The selected output goes LOW (0V) while the others stay HIGH (VCC), making it perfect for driving PNP transistors or active-low chip-select pins.

• Breadboard Ready: Standard DIP-16 package for easy prototyping.

Technical Specifications

Popular Use Cases

• I/O Expansion: Control 8 LEDs or Relays using only 3 digital pins.

• Memory Addressing: Selecting specific memory banks in vintage computer builds.

• 7-Segment Displays: Multiplexing multiple displays to reduce pin count.

• Digital Switching: Routing data signals to different parts of a circuit.