Octal-to-Binary take 8 inputs and provides 3 outputs, thus doing the opposite of what the 3-to-8 decoder does. If a device output code has fewer bits than the input code has, the device is usually called an encoder. Out of M input lines only one is activated at a time and produces equivalent code on output N lines. An encoder has M input and N output lines. They accept one or more inputs and generate a multibit output code.Įncoders perform exactly reverse operation than decoder. Encoders are combinational logic circuits and they are exactly opposite of decoders. The purpose of encoder is standardization, speed, secrecy, security, or saving space by shrinking size. The truth table is as follows:Īn encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another. It is also called as binary to octal decoder it takes a 3-bit binary input code and activates one of the 8(octal) outputs corresponding to that code. For active- low outputs, NAND gates are used. It uses all AND gates, and therefore, the outputs are active- high. 3-to-8-line decoder constructed from two 2-to-4-line decoders.ĭecoder with enable input can function as demultiplexer. The low value at the output represents the state of the input.Ĭombine two or more small decoders with enable inputs to form a larger decoder e.g. The truth table for this decoder is shown below:įor any input combination only one of the outputs is low and all others are high. They will give rise to 4 states A, A’, B, B’.
Let us suppose that a logic network has 2 inputs A and B. The output indicates presence or absence of specific number at the decoder input. The input to a decoder is parallel binary number and it is used to detect the presence of a particular binary number at the input. 2-to-4 decoder, 3-to-8 decoder or 4-to-16 decoder are other examples.
In case the 'n' bit coded information has unused bit combinations, the decoder may have less than 2n outputs. These types of decoders are combinational circuits that convert binary information from 'n' coded inputs to a maximum of 2n unique outputs. Such output is called as "active low output".Ī slightly more complex decoder would be the n-to-2n type binary decoders. If instead of AND gate, the NAND gate is connected the output will be "Low" (0) only when all its inputs are "High". The example decoder circuit would be an AND gate because the output of an AND gate is "High" (1) only when all its inputs are "High." Such output is called as "active High output".
Decoding is necessary in applications such as data multiplexing, 7 segment display and memory address decoding. In digital electronics, a decoder can take the form of a multiple-input, multiple-output logic circuit that converts coded inputs into coded outputs, where the input and output codes are different e.g.
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