8 TO 3 PRIORITY ENCODER
8 TO 3 PRIORITY ENCODER
This kind of encoder is also named an 8-bit or Octal to Binary priority encoder. This type of encoder consists of 8 inputs and 3 outputs. When multiple inputs are active high at the same time, the input with the highest priority is considered to represent the output.
For example, if D1, D2, and D3 inputs are active high or logic 1 regardless of other input bits, then the encoded output of the priority encoder will be D3 i.,e 111. Here, the D1, and D2 input bits are either irrelevant or don’t care conditions.
The 8 to 3 priority encoder truth table is shown below.
D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | A | B | C |
0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
0 | 0 | 0 | 0 | 0 | 0 | 1 | X | 0 | 0 | 1 |
| 0 | 0 | 0 | 0 | 0 | 1 | X | X | 0 | 1 | 0 |
| 0 | 0 | 0 | 0 | 1 | X | X | X | 0 | 1 | 1 |
0 | 0 | 0 | 1 | X | X | X | X | 1 | 0 | 0 |
| 0 | 0 | 1 | X | X | X | X | X | 1 | 0 | 1 |
0 | 1 | X | X | X | X | X | X | 1 | 1 | 0 |
| 1 | X | X | X | X | X | X | X | 1 | 1 | 1 |
From the above truth table, we can observe that D0, D1, D2, D3, D4, D5, D6, D7 are the inputs, and A, B, C are the outputs of an 8 to 3 priority encoder.
