Encoders: A Detailed Discussion
An Encoder is a combinational circuit that converts an active input signal into a corresponding binary code output. It is essentially the reverse operation of a Decoder.
In simpler terms, an Encoder takes multiple input lines and encodes them into a smaller number of output lines. It is used to represent data in a more compact form.
🧠 Introduction to Encoders
- An Encoder is a device that has 2^n input lines and produces an n-bit binary code output.
- An n-input encoder will generate n-bit output, typically in binary form.
Basic Definition:
An Encoder is a digital circuit that converts 2^n input lines into an n-bit binary output. Only one input is active at a time (in most cases), and the corresponding output is the binary representation of the active input.
🎯 Types of Encoders
There are two main types of Encoders:
- Priority Encoder
- Binary Encoder
1️⃣ Binary Encoder
- A Binary Encoder encodes a single active input into a binary code based on the input line number.
- It typically takes 2^n input lines and generates an n-bit output.
Truth Table for 4×2 Binary Encoder:
| I₃ | I₂ | I₁ | I₀ | O₁ | O₀ |
|---|---|---|---|---|---|
| 0 | 0 | 0 | 1 | 0 | 0 |
| 0 | 0 | 1 | 0 | 0 | 1 |
| 0 | 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 0 | 0 | 1 | 1 |
- In the above table, I₃, I₂, I₁, I₀ are the inputs, and O₁, O₀ are the binary output values.
- The highest priority input gets encoded first (if more than one input is active).
2️⃣ Priority Encoder
- A Priority Encoder is a modified binary encoder that assigns a priority to the inputs.
- The highest priority input is encoded first, and if more than one input is active at the same time, only the highest-priority input will be encoded.
Truth Table for 4×2 Priority Encoder:
| I₃ | I₂ | I₁ | I₀ | O₁ | O₀ | V |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 1 | 0 | 0 | 1 |
| 0 | 0 | 1 | 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 0 | 1 | 0 | 1 |
| 1 | 0 | 0 | 0 | 1 | 1 | 1 |
- V is the validity bit, which is set to 1 when there is at least one active input.
🔧 Working of Encoders
1. Basic Working:
- For a given n-input encoder, only one input can be active at a time (usually).
- The encoder assigns a binary code to the active input line based on its position.
2. Priority Encoder Working:
- If multiple inputs are active simultaneously, the encoder outputs the binary code corresponding to the highest-priority active input.
⚙️ Applications of Encoders
Encoders are widely used in various fields of digital electronics and computing. Some common applications include:
- Data Compression: Encoders are used to reduce the number of bits needed to represent data.
- Digital Communication Systems: In communication systems, encoders convert messages into a format that can be easily transmitted over a channel.
- Keyboard Encoding: In computer keyboards, a key encoder encodes keypresses into a corresponding binary code for the computer.
- Address Encoding in Memory Systems: Encoders help in converting multiple input lines (address lines) into a smaller binary code for efficient memory addressing.
🔥 Example Problem
Let’s say we need to design a 4×2 binary encoder:
Inputs: I₃, I₂, I₁, I₀ (4 input lines)
Outputs: O₁, O₀ (2 output lines)
The output must produce a binary code corresponding to the highest active input. If no input is active, the output is 00.
Solution:
- When I₃ is active, the output will be 11 (since 3 in binary is 11).
- When I₂ is active, the output will be 10 (since 2 in binary is 10).
- When I₁ is active, the output will be 01 (since 1 in binary is 01).
- When I₀ is active, the output will be 00 (since 0 in binary is 00).
📝 Summary
| Feature | Encoder |
|---|---|
| Function | Converts inputs to binary code |
| Inputs | 2^n inputs |
| Outputs | n-bit binary output |
| Types | Binary Encoder, Priority Encoder |
| Applications | Data compression, communication, keyboard encoding, memory addressing |
🌟 Key Takeaways:
- Encoders convert multiple inputs into a compact binary code output.
- Priority Encoders handle multiple active inputs by assigning priority to the highest active input.
- Encoders are widely used in digital communication systems, keyboards, and data compression.