Content deleted Content added
Clarify that the code example gives the LSB the highest priority, unlike the image at the top which gives the MSB I(3) the highest priority. |
add ==Implementation==, move circuit after truth table |
||
Line 4:
Applications of priority encoders include their use in [[Programmable interrupt controller|interrupt controllers]] (to allow some [[interrupt request]]s to have higher priority than others), decimal or [[binary encoding]], and [[Analog-to-digital converter|analog-to-digital]] / [[Digital-to-analog converter|digital to-analog]] conversion.<ref>{{cite book |title=The TTL Applications Handbook |date=August 1973 |publisher=Fairchild Semiconductor |page=4-4}}</ref>
==Implementation==
[[File:A 4-2 Priority Encoder .jpg|alt=Gate-level diagram of a single bit 4-to-2 Priority Encoder|thumb|486x486px|[[Logic gate|Gate-level]] diagram of a single bit 4-to-2 priority encoder. I(3) has the highest priority.|center]]▼
A [[truth table]] of a single bit 4-to-2 priority encoder is shown, where the inputs are shown in decreasing order of priority left-to-right, and "x" indicates a [[don't care term]] - i.e. any input value there yields the same output since it is superseded by a higher-priority input. The (usually-included{{efn|For instance, the [[List of 7400-series integrated circuits|74x147]] 10-to-4 [[BCD (character encoding)|BCD]] priority encoder does not have a dedicated output valid signal. However, invalid is indicated by all outputs simultaneously high. https://www.ti.com/lit/ds/symlink/sn74ls148.pdf}}) "v" output indicates if the input is valid.
Line 33 ⟶ 32:
|style="background:#bfd; color:black; border-left:2px solid #000;"|1 || {{yes2|1}} || {{yes2|1}}
|}
▲[[File:A 4-2 Priority Encoder .jpg|alt=Gate-level diagram of a single bit 4-to-2 Priority Encoder|thumb|486x486px|[[Logic gate|Gate-level]] diagram of a single bit 4-to-2 priority encoder. I(3) has the highest priority.|center]]
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.
| |||