定时器模拟PWM发生
.................\PWM
.................\PWM.M51
.................\PWM.hex
.................\PWM.lnp
.................\PWM.plg
.................\PWM.uvopt
.................\PWM.uvproj
.................\PWM_uvopt.bak
.................\PWM_uvproj.bak
.................\STARTUP.A51
.................\STARTUP.LST
.................\STARTUP.OBJ
.................\main.LST
.................\main.OBJ
.................\main.c