1.单片机的INT0引脚上连接了一个按键，按键的一端接地，另一端通过上拉电阻连接到INT0，对按键被按下的事件计数，并且在3个8段数码管上显示出来。另一个普通I/O引脚上连接一个按键用于清零计数，当计数达到999或者清零按键按下时，数码管被归零，重新开始计数。

2.硬件电路要求：单片机使用P1口驱动3位7段共阳极数码管，使用P2.0—P2.2口选择用于显示的数码管，外部中断引脚INT0(P3.2) 上连接了按键S1，用于中断计数，外部引脚P3.5(T1)上连接了按键S2，用于清零计数。

-1. Single chip microcomputer INT0 pin connection on a key, keys at one end of the ground, on the other end through resistor connected to the INT0, the counting of button is pressed, and in three eight digital tube display. Another common I/O pins connected a button to reset the count, when the count reaches 999 or reset button press, digital tube is zero, start counting again.

2. The hardware circuit requirements: MCU use P1 mouth driver three seven segment digital tube, a total of anode using P2.0- P2.2 choice for display of digital tube, external interrupt pin INT0 S1 (P3.2) connection on the buttons, used to interrupt count, external pins P3.5 S2 (T1) connection on the buttons, used for zero count.