VB读保持寄存器程序如下：
'读单个/多个保持寄存器，功能码03
Dim RunStr(7) As Byte
RunStr(0) = &H2 '从站号是02
RunStr(1) = &H3 '读单个/多个保持寄存器，03
RunStr(2) = &H0 '起始地址高字节
RunStr(3) = &H0 '起始地址低字节
RunStr(4) = &H0 '读取的寄存器数高8位
RunStr(5) = &H1 '读取的寄存器数低8位

Call crc16(RunStr(), 5)
RunStr(6) = HiByte
RunStr(7) = LoByte
'写命令发送后,当接收到7个字节时中断
CmdLenth = 7
MSComm1.RThreshold = CmdLenth
MSComm1.InBufferCount = 0
MSComm1.Output = RunStr
CommFlag = 1