Understanding Logic Circuits and Code Conversion

The question asks to identify a specific type of multiple-input, multiple-output logic circuit that performs code conversion, where the input and output codes are different. Let's examine the options provided and see which one best fits this description.

What is a Decoder?

A decoder is a combinational logic circuit that converts binary information from n input lines to a maximum of $2^n$ unique output lines. Typically, only one output line is active at any given time, corresponding to the binary code applied to the inputs.

For example, a 3-to-8 decoder has 3 input lines (say A, B, C) and 8 output lines (Y0 to Y7). If the input code is 010 (binary for 2), the output line Y2 will be active, while all other outputs are inactive. Here, the input is a 3-bit binary code, and the output can be seen as an 8-bit code where only one bit is high (a one-hot code). The input code (binary) and the output code (one-hot) are different.

Thus, a decoder takes a coded input (n-bit binary) and converts it into a different coded output ($2^n$-bit one-hot), acting as a multiple-input, multiple-output circuit (n inputs, $2^n$ outputs).

Examining Other Options

• Demultiplexer (Demux): A demultiplexer takes a single data input and a set of select inputs. Based on the binary code applied to the select inputs, it routes the data input to one of several output lines. Its primary function is data distribution, not code conversion in the sense described. It has one data input, multiple select inputs, and multiple outputs.
• Multiplexer (Mux): A multiplexer takes several data inputs and a set of select inputs. Based on the binary code applied to the select inputs, it selects one of the data inputs and routes it to a single output line. Its primary function is data selection, not code conversion. It has multiple data inputs, multiple select inputs, and one output.
• Encoder: An encoder performs the reverse operation of a decoder. It converts information from $2^n$ input lines (usually only one is active) into a n-bit binary code. For example, an 8-to-3 encoder takes 8 input lines and produces a 3-bit binary output. If input line I5 is active, the output will be 101 (binary for 5). It converts a coded input (one-hot) to a different coded output (binary), and it is a multiple-input, multiple-output circuit ($2^n$ inputs, n outputs).

Comparing Decoder and Encoder with the Description

Both decoders and encoders convert coded inputs into coded outputs where the codes are different. However, the phrasing "converts coded inputs into coded outputs" more naturally aligns with applying an input code (like a binary number) to the input terminals and getting a different code (like a one-hot representation) on the output terminals, which is the standard view of a decoder (binary input code to one-hot output code).

While an encoder also performs code conversion, the standard description often focuses on its inputs being separate lines (like activated buttons) that are converted into a binary code output.

Considering the options and the common usage of these terms, the description most closely matches the function of a decoder, which converts a binary input code into a one-hot output code.

Conclusion on Logic Circuit Type

Based on the definition and function, a logic circuit that is a multiple-input, multiple-output circuit converting coded inputs into coded outputs where the input and output codes are different is a decoder. While an encoder also fits parts of the description, a decoder is the most direct match for converting a binary input code to a different coded output like a one-hot code.