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本刊1989年第10期第45页刊出的《一种能直接算示电感值的555定时电路》一文在电路设计上存在错误,不能正常工作。由《DATA BOOK》提供的4518计数器芯片的真值表及引脚功能如图1所示。由图1可见,该计算器有两个计数状态:1)使能端为高电平,置零端为低电平,则对时钟端信号的上升沿计数;2)时钟端为低电平,置零端为低电平,则对使能端信号的下跳沿计数。原文显然是将4518内的A、B 两个计数器分别置
The article published in 1989, No. 10, page 45, “a kind of direct calculation of inductance 555 timer circuit,” a text in the circuit design errors, can not work properly. The truth table and pin functions of the 4518 counter chip provided by “DATA BOOK” are shown in FIG. 1. Can be seen from Figure 1, the calculator has two count states: 1) enables high end, set zero end is low, then the rising edge of the clock signal count; 2) the clock is low , Set to zero for the low end of the next signal on the edge of the count enable. The original is obviously the 4518 within the A, B two counters were set