🔲 74238 IC – Dual 4-to-16 Line Decoder / Demultiplexer (DIP-24)
The 74238 is a dual 4-line to 16-line decoder/demultiplexer, meaning it contains two independent 4-to-16 line decoders in one IC. Each decoder has 4 binary select inputs, one active-LOW enable input, and 16 active-LOW outputs. Only one output goes LOW at a time based on the binary input, making it ideal for address decoding, memory selection, and control signal demultiplexing.
⚙️ Technical Specifications
| Parameter | Specification |
|---|
| Logic Family | TTL (74 series) |
| Function | Dual 4-to-16 Decoder/Demux |
| Inputs per Decoder | 4 Data + 1 Enable |
| Outputs per Decoder | 16 (Active LOW) |
| Total Decoders | 2 |
| Package Type | DIP-24 |
| Supply Voltage (Vcc) | 4.75V to 5.25V (typically 5V) |
| Input Logic Levels | HIGH ≥ 2V, LOW ≤ 0.8V |
| Output Logic Levels | Active LOW (open collector/TTL) |
| Operating Temperature | 0°C to +70°C |
📌 Function Overview
Each decoder takes 4-bit binary inputs (A0 to A3) and selects one out of 16 output lines by setting it LOW, while the others remain HIGH.
🧠 Example: Binary Input to Output Mapping
| A3 | A2 | A1 | A0 | Output (Active LOW) |
|---|
| 0 | 0 | 0 | 0 | O0 = LOW |
| 0 | 0 | 0 | 1 | O1 = LOW |
| 1 | 1 | 1 | 1 | O15 = LOW |
All other outputs remain HIGH.
🛠️ Applications
Memory address decoding
Microprocessor I/O selection
LED multiplexing
Data routing and bus control
Control logic in embedded systems
