独立键盘在单片机上的一个实现。利用TIMER0中断，CPU在不停的扫描程序，60ms到，执行按键驱动，函数在48ms执行一次，60ms再次执行，避免了CPU资源的浪费。-Independent on the keyboard in a single-chip implementation. Use TIMER0 interrupt, CPU in constant scanner, 60ms that the implementation of key drivers, perform a fu