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几乎每一台PC机都配置有打印口,但它一般都用作连接打印机的输出口.这里向大家介绍一种十分简单的方法,不需要制作或增加任何硬件电路,只需对原有的打印口作一处改动,即可使之成为通用的并行I/O口.从PC机打印口的电路图(它在许多PC机的书籍中都有介绍,这里就不再画出)中可以看出,数据输入缓冲器U3(74LS244)的输入端与数据输出锁存器U4的输出端都与25芯插座的2—9端相连,由于U4(74LS374)的1脚((?))始终接地,其输出端不能处于高阻状态,这样便影响了通过25芯插座2—9端输入数据,所以PC机打印口一般只能用作输出口而不能用作通用的输入口.
Almost every PC is equipped with a print port, but it is generally used to connect the printer’s output port. Here to introduce a very simple method, do not need to make or add any hardware circuit, only the original Print port make a change, you can make it a common parallel I / O port from the PC printer port circuit diagram (which in many PC books have introduced, no longer drawn here) can see , The input of data input buffer U3 (74LS244) and the output of data output latch U4 are connected to the 2-9 terminals of the 25-pin socket. Since 1 pin (?) Of U4 (74LS374) is always grounded , The output can not be in a high impedance state, which will affect the input data through the 25-pin socket 2-9 end, so the PC printer port generally can only be used as an output port and can not be used as a universal input port.