| 摘要 |
The electronic BCD 8421 up/down counter of the invention is a synchronously driven counter which consists of decades according to Figure 3. To avoid ambiguities, all dual flip flops are shown as dual flip flops. The decades of this BCD 8421 counter can be switched by means of the selection circuits (71-74, 72-75 and 73-76) and the flip flop input circuit (55) and the AND gates (81 and 82). The line (1) for the decades of this counter is also pre-selected via an AND gate (86) so that the nine-zero and zero-nine position changes can be achieved in the simplest possible manner. If necessary, this up/down counter is constructed in accordance with Figure 4. The input circuit (55) is different in Figure 4. <IMAGE>
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