用VC++编写的dll文件，方便上位机编写应用程序ModbusPCOM.dll，借用pcomm.dll实现sio read write, 内置了CRC16效验，实现了modbus01,03,05,06,16功能。 debug和Release目录下都有简单的测试应用程序-Written by VC++ dll files to facilitate the preparation of PC applications ModbusPCOM.dll, borrow pcomm.dll achie