通过环路串口判断串行通信电平转换芯片功能是否正常，并通过读写DRAM 判断硬件。...

代码说明：

通过环路串口判断串行通信电平转换芯片功能是否正常，并通过读写DRAM 判断硬件。-Through the loop to determine serial communication serial port level translator chip features and whether it is normal, and through reading and writing DRAM hardware judge.