.用单片机的定时器和计数器设计一个秒表，LED采用BCD码显示，发光二极管亮表示0，暗表示1，从零开始计时，记到99后从头开始，依次循环，时间间隔为900ms，要求采用定时器0工作于工作方式2。-With the design of single-chip timers and counters a stopwatch, LED BCD code display, light emitting diode light 0, dark one, the timing of starting from scratch, remember to start from scratch to 99, followed by cycle, the time interval of 900ms, requires Timer 0 is at work 2.