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在微机实时控制中,控制信号的输出是通过I/O接口电路实现的。常用的有8255、Z80-PIO等接口芯片。这些芯片的输出端口均为双向的三态门。在使用这些芯片时,如果不注意其高阻状态,即通常所说的悬空状态,就会将悬空状态输出,造成误输出。图1实线所示为一接口芯片控制继电器的常用电路。采用这种控制电路时,接口芯片的端口是不允许出现悬空状态的。一旦端口悬空,其隔离非门的输入端就相当于输入了一个高电平信号,因此会使继电器吸合,造成误动作。而当接口芯片的控制软件程序没
In computer real-time control, the control signal output is realized through the I / O interface circuit. Commonly used 8255, Z80-PIO interface chip. The output ports of these chips are bi-directional tri-state gates. In the use of these chips, if you do not pay attention to its high-impedance state, that is, the so-called dangling state, it will be suspended state output, resulting in erroneous output. Figure 1 shows a solid line interface chip control relay commonly used circuits. Using this control circuit, the interface chip port is not allowed to appear vacant state. Once the port is left open, the isolated input of the NOR gate is equivalent to a high-level signal input, so the relay will pull, resulting in malfunction. And when the interface chip control software program did not