The priority encoder is an improvement on a simple encoder circuit, in terms of handling all possible input configurations. Priority encoders can be easily connected in arrays to make larger encoders, such as one 16-to-4 encoder made from six 4-to-2 priority encoders - four 4-to-2 encoders having the signal source connected to their inputs, and the two remaining encoders take the output of the first four as input.
The (usually-included ) "v" output indicates if the input is valid. any input value there yields the same output since it is superseded by higher-priority input.
An example of a single bit 4 to 2 encoder is shown, where highest-priority inputs are to the left and "x" indicates an irrelevant value - i.e. If two or more inputs are given at the same time, the input having the highest priority will take precedence.
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