说明：  汇编程序，附加proteus仿真电路，8253的应用。8253芯片是可编程计数器/定时器。这种芯片外形引脚都是兼容性的。8253内部有三个计数器，分别称为计数器0、计数器1和计数器2，他们的机构完全相同。
(Assembler, additional proteus simulation circuit, 8253 application. 8253 chip is a programmable counter / timer. This kind of chip shape and pin are compatible. There are three counters in 8253, which are called counter 0, counter 1 and counter 2. Their mechanisms are exactly the same.)