双数码管可调秒表，，选用12MHz的晶体。为了达到精确计时，选用定时器方式2，每计数250重载一次，即250us，定义一整数变量计数重载次数，这样计数4000次即为一秒。定义两个字节变量S10和S1分别计算秒十位和秒个位。-Dual adjustable digital stopwatch,, use 12MHz crystal. In order to achieve accurate timing, use the timer mode 2, one for each count of 250 heavy, that is 250us, define an integer variable counting the number of overloaded, so that 4000 is the second count. Define two bytes of variables were calculated S10 and S1 ten seconds, and seconds bit.