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An encoder is a device used to change a signal (such as a bitstream) or data into a code. The code may serve any of a number of purposes such as compressing information for transmission or storage, encrypting or adding redundancies to the input code, or translating from one code to another. This is usually done by means of a programmed algorithm, especially if any part is digital, while most analog encoding is done with analog circuitry.
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Single bit 4 to 2 Encoder
An encoder has 2n input lines and n output lines.The output lines generate a binary code corresponding to the input value. For example a single bit 4 to 2 encoder takes in 4 bits and outputs 2 bits. It is assumed that there are only 4 types of input signals these are : 0001, 0010, 0100, 1000.
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| 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 |
The encoder has the limitation that only one input can be active at any given time. If two inputs are simultaneously active, the output produces an undefined combination. To prevent this we make use of the priority encoder.
Priority encoder
A priority encoder is such that if two or more inputs is given at the same time, the input having the highest priority will take precedence. An example of a single bit 4 to 2 encoder is shown.
| I3 | I2 | I1 | I0 | O1 | O0 |
|---|---|---|---|---|---|
| 0 | 0 | 0 | d | 0 | 0 |
| 0 | 0 | 1 | d | 0 | 1 |
| 0 | 1 | d | d | 1 | 0 |
| 1 | d | d | d | 1 | 1 |
Connecting Priority Encoders
Priority encoders can be easily connected in arrays to make larger encoders, such as a 16 to 4 encoder made from six 4 to 2 priority encoders (four encoders having the signal source connected to their inputs, and two encoders that take the output of the first four as input).
Examples
- A compressor encodes data (e.g., audio/video/images) into a smaller form.
- A multiplexer combines multiple inputs into one output.
- A rotary encoder converts rotary position to an analog (e.g., analog quadrature) or digital (e.g., digital quadrature, 32-bit parallel, or USB) electronic signal.
- A linear encoder similarly converts linear position to an electronic signal.
See also
External links
 |
Look up Encoder in Wiktionary, the free dictionary. |
- Encoding data to an ID Card: Using a Magnetic Stripe Encoder
- Absolute Encoder Using Gray Code - Absolute encoding for rotating shaft, with a comprehensive discussion of gray code.
- asic-world's Digital Combinational Logic (part III) - an overview of encoders in circuitry.
Wikipedia content modification information:
- This page was last modified on 7 December 2008, at 21:39.
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