The case statement is a cleaner way to express multi-way branches than a long if/else if chain, especially when every branch depends on the exact value of one signal. A decoder — which activates exactly one of many outputs based on a binary-encoded input — is a textbook use case.
Build a circuit with a 3-bit input in and an 8-bit output out. Exactly one bit of out should be 1: bit number in (the rest should be 0).
Interface
| Signal | Direction | Width | Description |
|---|---|---|---|
in |
input | 3 | Binary-encoded index, 0-7 |
out |
output | 8 | One-hot: out[in] = 1, all other bits 0 |
Examples
| in | out (binary) |
|---|---|
| 0 | 00000001 |
| 3 | 00001000 |
| 7 | 10000000 |
Notes
- Use
always @(*)with acase (in)statement, one branch per value ofin(0 through 7). - Declare
outasoutput regsince it’s assigned inside a procedural block.