例1:试用两片74LS148设计一个16-4线优先编码器。允许附加必要的门电路。
解:根据优先编码器的逻辑功能,列出16-4线优先编码器的逻辑功能表如表1。~为编码输入端,其中的优先级最高,的优先级最低。~为编码输出端。输入输出均为低电平有效。
表1 16-4线优先编码器逻辑功能表
全站搜索
输入 | 输出 | ||||||||||||||||||
A0 | A1 | A2 | A3 | A4 | A5 | A6 | A7 | A8 | A9 | A10 | A11 | A12 | A13 | A14 | A15 | Z3 | Z2 | Z1 | Z0 |
× | × | × | × | × | × | × | × | × | × | × | × | × | × | × | 0 | 0 | 0 | 0 | 0 |
× | × | × | × | × | × | × | × | × | × | × | × | × | × | 0 | 1 | 0 | 0 | 0 | 1 |
× | × | × | × | × | × | × | × | × | × | × | × | × | 0 | 1 | 1 | 0 | 0 | 1 | 0 |
× | × | × | × | × | × | × | × | × | × | × | × | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 |
× | × | × | × | × | × | × | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 0 |
× | × | × | × | × | × | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 1 |
× | × | × | × | × | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 |
× | × | × | × | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 |
× | × | × | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 |
× | × | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 |
× | × | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 |
× | × | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 |
× | × | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 |
× | × | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 |
× | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |