定时器控制流水灯高低4位交替闪烁 中断方式T0模式2，内有Keil C源文件，已编译通过；内有Proteus仿真文件(DSN)，已仿真通过。(Timer control flow light high and low 4-bit alternate flashing interrupt mode t0 mode 2, with keil c source file inside, compiled; proteus simulation