C8051F020单片机的I/O测试程序，最基本的端口测试，运行后P1-P7口出现低频方波，可用来检测最小系统能否正常工作。-C8051F020 MCU I/O testing procedures, the most basic port test, running P1-P7 I appear low-frequency square-wave can be used to detect the smallest system can work properly.