UART和RS232/RS485的关系是什么？https://blog.csdn.net/u013178472/article/details/81226780?ops_request_misc=&request_id=&biz_id=102&utm_term=%E4%B8%B2%E5%8F%A3%E5%92%8Crs485&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduweb~default-4-.pc_search_similar&spm=1018.2226.3001.4187
