使用单片机端口驱动一位共阳极七段数码管，使数码管上依次显示1,2. 3.8.,9,0,9,8,7,..3,2,1,2,3.如此无限显示，且要求每个数字显示大约持续1秒钟。绘制系统硬件电路并编写控制程序。
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