说明：  c8051,此程序可完成CP0比较器的比较功能，比较器CP0+来自于VREF引脚,CP0-由S2控制.按下S3后,比较器响应后将产生中断,可在中断程序中设断点观察.
(c8051, this program can complete the comparison function CP0 comparator, the comparator CP0+ from VREF pin, CP0-controlled by the S2. Press the S3, the comparator will generate an interrupt response, the program can set a breakpoint in the interrupt observation.)