Private Sub cmdSDO_Click() Dim btSend(8) As Byte
btSend(0) = &H1 '目标站号 btSend(1) = &H5 '功能码
btSend(2) = &H0 'Q1.1地址（0009）高字节 btSend(3) = &H9 'Q1.1地址（0009）低字节 btSend(4) = &HFF '强制值高字节 btSend(5) = &H0 '强制值低字节
Dim crc
Dim btCRCHi As Byte, btCRCLo As Byte
crc = CalCRC16Fast(btSend, 6, btCRCLo, btCRCHi)
btSend(6) = btCRCHi btSend(7) = btCRCLo
ComK3.Output = CVar(btSend)
End Sub
④ “读取IB0”按钮单击事件
'查表知I0.0的modbus地址为0000，从I0.0开始读取连续8位 Private Sub Command1_Click()
'发请求
Dim btSend(8) As Byte
btSend(0) = &H1 '目标站号 btSend(1) = &H2 '功能码
btSend(2) = &H0 'I0.0地址（0000）高字节 btSend(3) = &H0 'i0.0地址（0000）低字节 btSend(4) = &H0 '读取个数高字节 btSend(5) = &H8 '读取个数低字节
Dim crc
Dim btCRCHi As Byte, btCRCLo As Byte
crc = CalCRC16Fast(btSend, 6, btCRCLo, btCRCHi)
btSend(6) = btCRCHi btSend(7) = btCRCLo
ComK3.Output = CVar(btSend)
'注意下面编写的接收过程很简单，要编写实际应用的监控程序来说需要更完善 Dim btReceive As Variant
With ComK3 Do
DoEvents
Loop Until .InBufferCount = 6
.InputLen = 6
btReceive = .Input
If btReceive(1) = &H2 Then '若正确，返回帧的第2个字节为功能码.实际上，此处应首先进行CRC校验
txtReceive.Text = Hex$(btReceive(3)) End If End With End Sub