真值表:
| EN | X3 | X2 | X1 | X0 | EF | Y1 | Y0 |
| 0 | X | X | X | X | 1 | 0 | 0 |
| 1 | 1 | X | X | X | 0 | 1 | 1 |
| 1 | 0 | 1 | X | X | 0 | 1 | 0 |
| 1 | 0 | 0 | 1 | X | 0 | 0 | 1 |
| 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
| EN | X3 | X2 | X1 | X0 | EF | Y1 | Y0 |
| 0 | X | X | X | X | 1 | 0 | 0 |
| 1 | 1 | X | X | X | 0 | 1 | 1 |
| 1 | 0 | 1 | X | X | 0 | 1 | 0 |
| 1 | 0 | 0 | 1 | X | 0 | 0 | 1 |
| 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 |

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