Description

The 74148 8-Line to 3-Line Priority Encoder is a high-speed TTL logic IC designed to encode multiple inputs into a smaller set of binary outputs based on priority. This IC accepts eight active LOW inputs (0–7) and outputs a 3-bit binary code representing the highest-priority active input. Housed in a 16-pin Dual Inline Package (DIP), the 74148 is widely used in keypad encoding, microcontroller interfaces, digital control systems, and priority-based signal processing applications.

Priority encoders like the 74148 are essential in systems where multiple simultaneous input signals may occur, but only the highest-priority input should be represented at the output. By converting multiple input lines into fewer outputs, the IC reduces wiring complexity and simplifies digital circuit design, while ensuring accurate priority-based decision-making.

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⚙️ Key Features:

• Function: 8-Line to 3-Line Priority Encoder (active LOW inputs)

• Logic Family: TTL

• Inputs: 8 active LOW inputs (0–7)

• Outputs: 3-bit binary output (A, B, C) representing the highest-priority active input

• Active Low Inputs: Logic LOW indicates an active input

• Priority Function: Highest-numbered active input is encoded

• Operating Voltage: 4.75V – 5.25V (TTL standard)

• Low Power Consumption: Efficient for TTL digital circuits

• Standard 16-Pin DIP Package: Easy for breadboard prototyping and PCB design

• Carry Output / Enable: Can cascade multiple encoders for larger input systems

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🧩 Pin Configuration (16-Pin DIP):

This configuration encodes up to 8 inputs into 3 output lines, with the highest active input taking priority, ensuring deterministic behavior when multiple inputs are active.

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⚡ Electrical Characteristics:

• Supply Voltage (VCC): 5V TTL standard

• Input High Voltage (VIH): ≥ 2V

• Input Low Voltage (VIL): ≤ 0.8V

• Output High Voltage (VOH): ≥ 2.4V

• Output Low Voltage (VOL): ≤ 0.4V

• Propagation Delay: ~25 ns typical

• Power Dissipation: ~50 mW

The TTL design ensures fast and reliable encoding, suitable for keypad scanning, priority control, and digital interface applications.

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🧠 How It Works:

The 74148 IC converts eight active-low inputs into a 3-bit binary output, following a priority rule:

• Highest-Numbered Active Input: Determines the output code

• Active Low Inputs: Input is considered active when LOW

• Enable / Carry Output: Allows cascading additional encoders for higher input ranges

• Binary Outputs (A–C): Represent the encoded value of the highest-priority input

By encoding multiple inputs into fewer outputs, the 74148 simplifies circuit design and ensures accurate, priority-based data representation.

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🛠️ Applications:

• Keypad Encoding – Convert multiple button presses into 3-bit binary output

• Microcontroller Interfaces – Reduce the number of input pins required

• Digital Priority Control Systems – Encode highest-priority signals efficiently

• Signal Multiplexing – Simplify wiring for multiple input channels

• Counters and Data Acquisition Systems – Encode sensor or switch inputs efficiently

• Educational Electronics Kits – Teach priority encoding and digital logic concepts

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💡 Advantages:

• Encodes 8 inputs into 3 output lines efficiently

• Priority handling ensures reliable output for simultaneous inputs

• TTL design ensures high-speed operation and easy integration

• Reduces component count and wiring complexity

• Can be cascaded for larger input systems

• Standard 16-pin DIP package is breadboard-friendly

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📦 Package Includes:

• 1 × 74148 8-Line to 3-Line Priority Encoder IC (DIP-16)

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📘 Conclusion:

The 74148 DIP 8-Line to 3-Line Priority Encoder is a high-performance, reliable IC for converting multiple active-low inputs into a 3-bit binary output with priority logic. Perfect for keypads, microcontroller systems, priority control circuits, and educational electronics, it provides a compact, versatile, and efficient solution for modern digital systems.