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A priority encoder is a circuit or algorithm that compresses multiple binary inputs into a smaller number of outputs. They are aften used to control interrupt requests by acting on the highest priority request.
If two or more inputs are 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, where highest-priority inputs are to the left and "x" indicates either a 1 or a 0 (i.e., either input value yields the same output when superseded by a higher-priority input).
{| class="wikitable" style="margin:0;"
!style="border-bottom:2px solid #000;"|I<sub>3</sub>
!style="border-bottom:2px solid #000;"|I<sub>2</sub>
!style="border-bottom:2px solid #000;"|I<sub>1</sub>
!style="border-bottom:2px solid #000;"|I<sub>0</sub>
!style="border-bottom:2px solid #000; border-left:2px solid #000;"| O<sub>1</sub>
!style="border-bottom:2px solid #000;"|O<sub>0</sub>
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| 0 || 0 || 0 || x ||style="border-left:2px solid #000;"| 0 || 0
|-
| 0 || 0 || 1 || x ||style="border-left:2px solid #000;"| 0 || 1
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| 0 || 1 || x || x ||style="border-left:2px solid #000;"| 1 || 0
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| 1 || x || x || x ||style="border-left:2px solid #000;"| 1 || 1
|}
{{caption|4 to 2 priority encoder}}
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).
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