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A decoder is a digital circuit that converts coded inputs into a specific set of output signals. It's essentially the inverse of an encoder. Decoders are used in various digital systems for tasks such as address decoding, data demultiplexing, and control signal generation.
Here are several types of decoders along with their explanations and implementations:
1. 2:4 Decoder:
A 2:4 decoder is a digital circuit that takes two input signals and produces four output signals.
It has two input lines (A and B) and four output lines (Y0, Y1, Y2, Y3).
The output lines are activated based on the binary value represented by the inputs.
Example Truth Table:
E | A1 | A0 | Y3 | Y2 | Y1 | Y0 |
O | X | X | 0 | 0 | 0 | 0 |
1 | 0 | 0 | 0 | 0 | 0 | 1 |
1 | 0 | 1 | 0 | 0 | 1 | 0 |
1 | 1 | 0 | 0 | 1 | 0 | 0 |
1 | 1 | 1 | 1 | 0 | 0 | 0 |
Implementation: A 2:4 decoder can be implemented using logic gates such as AND, OR, and NOT gates. Each output is connected to a specific combination of inputs to activate it.
1) Decoder with Active High/Low Output and Active High/Low Enable:
Decoders can have outputs that are either active high or active low, meaning they are activated when the output signal is at a logic high or low level, respectively.
Additionally, decoders can have an active high or active low enable input, which determines whether the decoder is enabled or disabled.
Implementation: Decoders with active high/low output and enable can be implemented using appropriate logic gates and flip-flops to control the output signals based on the input and enable conditions.
2) BCD to Seven Segment Display Decoder:
BCD (Binary-Coded Decimal) to Seven Segment Display Decoder is a specific type of decoder used to convert binary-coded decimal numbers into signals that can drive a seven-segment display.
BCD numbers range from 0000 to 1001 (0 to 9 in decimal).
A seven-segment display is a common type of display that can represent numbers (0-9) and some alphabets (A-F) using seven individually controlled segments.
Example Implementation:
Let's consider an example where we want to display BCD numbers (0-9) on a seven-segment display.
Truth Table:
A | B | C | D | a | b | c | d | e | f | g |
0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
0 | 0 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 |
0 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 |
0 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 |
0 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 1 |
0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 |
0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
1 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 |
Implementation: BCD to Seven Segment Display Decoder can be implemented using logic gates to generate the appropriate signals to light up the segments corresponding to the input BCD numbers. Each segment is controlled by a specific combination of inputs to display the corresponding digit on the seven-segment display.
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