摘要：单片机计数器，是集CPU ,RAM ,ROM ,定时，计数和多种接口于一体的微控制器。他体积小，成本低，功能强，广泛应用于智能产品和工业自动化上。而51系列单片机是各单片机中最为典型和最有代表性的一种。这次毕业设计通过对它的学习，应用，从而达到学习、设计、开发软、硬件的能力。

　　　这次毕业设计中，采用AT89S52单片机+0.36寸4位共阳数码管+5V继电器构成设计，加倒计时结束后声光的提示。倒计时返回位0-99.9S，最后小数点计时10下为1秒。可以任意设置倒计时时间。可以从0开始计时。同时具有秒表和倒计时功能。4个按键功能分别作为开始计时/暂停计时，以及倒计时时间增加减少，以及清零重新开始按钮。第一个按键是重新复位，重新开始计时;第二个按键是开始和暂停按键。计时的过程可以暂停，然后继续进行；第三个按键是时间增加按键，每次调整一秒；第四个按键是时间减少按键，每次调整一秒。

关键词：AT89S52单片机；共阳数码管；继电器；秒表；倒计时

ABSTRACT：Counter SCM, is a set of CPU, RAM, ROM, timing, counting and multiple interfaces in one microcontroller. His small size, low cost, strong function, widely used in intelligent products and industrial automation. And 51 Series SCM is the most typical and the most representative one. The graduation design through the study, application, to achieve the study, design, development software, hardware capabilities.

　　　This graduation design, using 52 single-chip +0.36inch of a total of 4 digital tube Yang +5V relay design, with the countdown to the end after the acousto-optic tips. Countdown to return to0-99.9S, finally the decimal point10for a second time. Can set the countdown time. From 0begin timing. At the same time with stopwatch and countdown function. 4function keys respectively as the start timing / pause time, and the countdown time increase decrease, and reset the start button. The first button is reset, start time; the second keys is the beginning and the pause button. Timing of the process allows you to pause, and then continue; third key time increase,adjust each one second; fourth keys are keys to adjust each time is reduced, a second.

Key words: AT89S52 Single Chip Microcomputer；Total Yang  Digital Tube；Relay；Stopwatch；Countdown