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74238 IC – Dual 4-to-16 Line Decoder / Demultiplexer (DIP-24)
🔲 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.
Outputs are active LOW
Enable must be LOW to activate decoding
Output = 0 when selected, others = 1
🧠 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