vb源程序，包括通讯串口信号 测试 ，收发 校验-vb source code, including the serial communications signal test, send and receive checksum

在IFIX组态软件中,采用VB编写GPRS通讯程序,与支持MODBUS协议的PLC进行数据通讯.-In IFIX configuration software, using VB, GPRS communication procedures, and support of MODBUS protocol PLC data communication.