Question

请问谁有VB编写modbus的应用例子，要详细些的，最近在学，很迷惑啊！

Answer 1

其实也很简单的，搞清楚功能码的作用，以及指令格式，和CRC校验就差不多了，如00 06 00 00 01 00 89 8B，00是从机地址，06是功能码的写，00 00 01 00是要发送的数据，89 8B是CRC校验码

Private Sub Command1_Click()
Dim CRC As String
Dim d() As Byte '待传输数据
Dim sendstr As String
Dim str As String
Dim N As Integer
Dim GetStr As String
Dim ErrMsg As String
Dim Status As Integer

'01 06 00 01 10 00
sendstr = Trim(Text1.Text)
strT = Split(sendstr, " ")
N = UBound(strT)
ReDim d(N)
For i = 0 To N
S = "&H" & strT(i)
d(i) = S
Next
' d(0) = &H1
' d(1) = &H6
' d(2) = &H0
' d(3) = &H0
' d(4) = &H10
' d(5) = &H0
CRC = CRC16(d) '调用CRC16计算函数
'CRC(0)为高位
'CRC(1)为低位
str = Text1.Text & " " & CRC
Text1.Text = str
Status = LynxSPcomm(MSComm1, str, True, GetStr, ErrMsg, True, 0)
Text2.Text = GetStr

End Sub
'注意：在数据传输时CRC的低位可能在前，而高位在后。

Function CRC16(data() As Byte) As String
Dim CRC16Lo As Byte, CRC16Hi As Byte 'CRC寄存器
Dim CL As Byte, CH As Byte '多项式码&HA001
Dim SaveHi As Byte, SaveLo As Byte
Dim i As Integer
Dim Flag As Integer
CRC16Lo = &HFF
CRC16Hi = &HFF
CL = &H1
CH = &HA0
For i = 0 To UBound(data)
CRC16Lo = CRC16Lo Xor data(i) '每一个数据与CRC寄存器进行异或
For Flag = 0 To 7
SaveHi = CRC16Hi
SaveLo = CRC16Lo
CRC16Hi = CRC16Hi \ 2 '高位右移一位
CRC16Lo = CRC16Lo \ 2 '低位右移一位
If ((SaveHi And &H1) = &H1) Then '如果高位字节最后一位为1
CRC16Lo = CRC16Lo Or &H80 '则低位字节右移后前面补1
End If '否则自动补0
If ((SaveLo And &H1) = &H1) Then '如果LSB为1，则与多项式码进行异或
CRC16Hi = CRC16Hi Xor CH
CRC16Lo = CRC16Lo Xor CL
End If
Next Flag
Next i
Dim ReturnData(1) As Byte
ReturnData(0) = CRC16Hi 'CRC高位
ReturnData(1) = CRC16Lo 'CRC低位

CRC16 = Hex(CRC16Lo) & " " & Hex(CRC16Hi)
End Function

追问

非常感谢！还有两个问题想进一步问一下：
1、我买了几个温湿度变送器，请问怎样确定它们的从机地址呢？
2、如果读取从机送来的温湿度数据，该用什么功能码呢？（看了一些文档，但对那几个不同的寄存器始终不太明白）