可调定时器C51Proteus仿真。

功能要求： 当按下K0第1次时，允许使用K1和K2对个位数进行增减，按下第K0第2次时，允许使用K1和K2对十位数进行增减，即K0在个位和十位间进行切换，K1和K2两个按键控制数码管数字加减，用K3进行确认后数码管自动加1计数。计数的范围从00到59间循环显示，每次计数到00时，蜂鸣器响3声。-Functional requirements: must adopt. When K0 first time, allowing the use of K1 and K2 on the single-digit increase or decrease, press the first K0 second time, allowing the use of K1 and K2 on the ten-digit increase or decrease, that K0 in the bit and 10 to switch between, K1 and K2 two digital control buttons to add and subtract, with K3 to confirm the digital tube automatically after a count. The count range is displayed in cycles　00 to 59, and the buzzer beeps three times each time the counter reaches 00.