一直看到有些朋友在问ModBus主从站的通讯问题，今天抽空儿给大家发几篇。
事先申明，我是调用的主从站库，库本身并不是我编写的，我没有那么大的能耐。
另外，上位机是用VB编写，VB本身不是很熟，如果有什么错误，请大家海谅。
最后，这仅仅只是一个测试程序，如果各位想用到商业方面，还需要各位自己去完善。
说明：plc从站，PC作主站，用ModBus协议进行通讯。PC机读取PLCVW区的数据；PC机还读取PLC内部I或者O地址的状态。
///////////////////////////////////////
以下是PLC程序实现，方便贴出，已转换为STL
TITLE=程序注释
Network 1 // 网络标题
// 在第一个循环周期内初始化Modbus从站协议
LD SM0.1
CALL SBR3, 1, 12, 9600, 0, 0, 128, 32, 1000, &VB0, M10.1, MB11
Network 2
// 在每个循环周期内执行Modbus 从站协议
LD SM0.0
CALL SBR1, M10.2, MB12
Network 3
LD SM0.0
MOVW AIW0, VW100
/I +54, VW100
MOVW AIW2, VW102
/I +54, VW102
MOVW AIW4, VW104
/I +54, VW104
MOVW AIW6, VW106
/I +54, VW106
Network 4
LD SM0.0
= Q0.0
Network 5
LD I0.0
= Q0.1
Network 6
LD I0.1
= Q0.2
///////////////////////////////////
以下是VB源码
Option Explicit
Private Declare Function GetTickCount Lib "kernel32" () As Long
Dim x1
Dim p11, p12, p13, p14, p15, p16, p17, p18
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 = ReturnData
End Function
Private Sub About_Click()
frmAbout.Show
End Sub
Private Sub Form_Load() '初始化
Timer1.Enabled = False '定时器1无效
Timer1.Interval = 1000 '定时器1时间为1S
Timer2.Enabled = True '定时器2有效
Timer2.Interval = 1000 '定时器2时间为1S
Text1.Text = ""
Text2.Text = ""
Text3.Text = ""
Text4.Text = ""
Text5.Text = ""
Text6.Text = ""
Text8.Text = ""
Text10.Text = ""
MSComm1.CommPort = 1 '设定端口号
MSComm1.Settings = "9600,n,8,1" '设定通讯波特率
MSComm1.InBufferSize = 1024 '接收缓冲器大小
MSComm1.OutBufferSize = 1024 '输出缓冲器大小
MSComm1.InputMode = comInputModeBinary '以二进制传输
MSComm1.RThreshold = 1 '
MSComm1.SThreshold = 0
MSComm1.InputLen = 0 '读取接收缓冲器所有字符
MSComm1.OutBufferCount = 0 '清空发送缓冲区
MSComm1.InBufferCount = 0 '清空接收缓冲区
If MSComm1.PortOpen = False Then
Command3.Caption = "打开串口"
Else
Command3.Caption = "关闭串口"
End If
End Sub
Private Sub Command1_Click()
Timer1.Enabled = True
End Sub
Private Sub Command2_Click() '退出程序，定时器1无效
Timer1.Enabled = False
Cls
Unload Me
End Sub
Private Sub Command3_Click()
On Error Resume Next
If MSComm1.PortOpen = False Then
MSComm1.PortOpen = True
Else
MSComm1.PortOpen = False
End If
If MSComm1.PortOpen Then '打开关闭按钮显示文字
Command3.Caption = "关闭串口"
Else
Command3.Caption = "打开串口"
End If
If Err Then '打开串口失败，则显示出错信息
MsgBox Error$, 48, "错误信息"
Exit Sub
End If
End Sub
Private Sub Timer1_Timer() '读V存储区数据
Dim CRC() As Byte
Dim FGetData As String
Dim aa() As Byte
Dim s As String
Dim str As String
Dim i As Integer
Dim bb, cc As String
ReDim aa(5) As Byte '定义动态数组
aa(0) = &HC
aa(1) = &H3
aa(2) = &H0
aa(3) = &H32
aa(4) = &H0
aa(5) = &H4
CRC = CRC16(aa)
str = CRC
s = ""
For i = 1 To LenB(str)
s = s + Hex(AscB(MidB(str, i, 1)))
Next i
bb = Right(s, 2)
cc = Mid(s, 1, 2)
If Len(s) < 4 Then
cc = Mid(s, 1, 1)
End If
ReDim Preserve aa(0 To 7) As Byte
aa(6) = Val("&H" & bb)
aa(7) = Val("&H" & cc)
MSComm1.OutBufferCount = 0 '清空输出寄存器
MSComm1.Output = aa
FGetData = ReceiveData
Text5.Text = FGetData
p11 = Val("&H" & Mid(FGetData, 7, 4))
p12 = Val("&H" & Mid(FGetData, 11, 4))
p13 = Val("&H" & Mid(FGetData, 15, 4))
p14 = Val("&H" & Mid(FGetData, 19, 4))
End Sub
Private Sub Command4_Click() 'I状态
Dim CRC() As Byte
Dim FGetData As String
Dim aa() As Byte
Dim s As String
Dim str As String
Dim i As Integer
Dim bb, cc As String
ReDim aa(5) As Byte '定义动态数组
aa(0) = &HC
aa(1) = &H2
aa(2) = &H0
aa(3) = &H0
aa(4) = &H0
aa(5) = &H1
CRC = CRC16(aa)
str = CRC
s = ""
For i = 1 To LenB(str)
s = s + Hex(AscB(MidB(str, i, 1)))
Next i
bb = Right(s, 2)
cc = Mid(s, 1, 2)
If Len(s) < 4 Then
cc = Mid(s, 1, 1)
End If
ReDim Preserve aa(0 To 7) As Byte
aa(6) = Val("&H" & bb)
aa(7) = Val("&H" & cc)
MSComm1.OutBufferCount = 0 '清空输出寄存器
MSComm1.Output = aa
FGetData = IReceiveData
p17 = Val("&H" & Mid(FGetData, 7, 2))
p18 = Val("&H" & Mid(FGetData, 9, 2))
End Sub
Private Sub Command5_Click() 'Q状态
Dim CRC() As Byte
Dim FGetData As String
Dim aa() As Byte
Dim s As String
Dim str As String
Dim i As Integer
Dim bb, cc As String
ReDim aa(5) As Byte '定义动态数组
aa(0) = &HC
aa(1) = &H1
aa(2) = &H0
aa(3) = &H0
aa(4) = &H0
aa(5) = &H1
CRC = CRC16(aa)
str = CRC
s = ""
For i = 1 To LenB(str)
s = s + Hex(AscB(MidB(str, i, 1)))
Next i
bb = Right(s, 2)
cc = Mid(s, 1, 2)
If Len(s) < 4 Then
cc = Mid(s, 1, 1)
End If
ReDim Preserve aa(0 To 7) As Byte
aa(6) = Val("&H" & bb)
aa(7) = Val("&H" & cc)
MSComm1.OutBufferCount = 0 '清空输出寄存器
MSComm1.Output = aa
FGetData = QReceiveData
p15 = Val("&H" & Mid(FGetData, 7, 2))
p16 = Val("&H" & Mid(FGetData, 9, 2))
End Sub
Private Function ReceiveData() As String '返回V存储器区数据
Dim FGetData As String
Dim t1 As Long
Dim av As Variant
Dim i As Integer
Dim ReDataLen As Integer
FGetData = ""
t1 = GetTickCount() '取时间，做延时用
Do '循环等待接收数据
DoEvents
If MSComm1.InBufferCount > 0 Then '串口有数据了
ReDataLen = MSComm1.InBufferCount '取数据长度
av = MSComm1.Input '将串口数据取出来
For i = 0 To ReDataLen - 1
FGetData = FGetData & Right("00" & Hex(av(i)), 2)
Next i
End If
If Len(FGetData) >= 6 Then
If Len(FGetData) > Val("&H" & Mid(FGetData, 5, 2)) * 2 + 8 Then
ReceiveData = FGetData
Exit Function
End If
End If
If GetTickCount - t1 > 2000 Then '2秒没收完就不收了
ReceiveData = ""
Exit Function
End If
Loop
End Function
Private Function IReceiveData() As String '反回I状态
Dim FGetData As String
Dim t1 As Long
Dim av As Variant
Dim i As Integer
Dim ReDataLen As Integer
FGetData = ""
t1 = GetTickCount() '取时间，做延时用
Do '循环等待接收数据
DoEvents
If MSComm1.InBufferCount > 0 Then '串口有数据了
ReDataLen = MSComm1.InBufferCount '取数据长度
av = MSComm1.Input '将串口数据取出来
For i = 0 To ReDataLen - 1
FGetData = FGetData & Right("00" & Hex(av(i)), 2)
Next i
End If
If Len(FGetData) >= 6 Then
If Len(FGetData) > Val("&H" & Mid(FGetData, 5, 2)) * 2 + 8 Then
IReceiveData = FGetData
Exit Function
End If
End If
If GetTickCount - t1 > 2000 Then '2秒没收完就不收了
IReceiveData = ""
Exit Function
End If
Loop
End Function
Private Function QReceiveData() As String '反回Q状态
Dim FGetData As String
Dim t1 As Long
Dim av As Variant
Dim i As Integer
Dim ReDataLen As Integer
FGetData = ""
t1 = GetTickCount() '取时间，做延时用
Do '循环等待接收数据
DoEvents
If MSComm1.InBufferCount > 0 Then '串口有数据了
ReDataLen = MSComm1.InBufferCount '取数据长度
av = MSComm1.Input '将串口数据取出来
For i = 0 To ReDataLen - 1
FGetData = FGetData & Right("00" & Hex(av(i)), 2)
Next i
End If
If Len(FGetData) >= 6 Then
If Len(FGetData) > Val("&H" & Mid(FGetData, 5, 2)) * 2 + 8 Then
QReceiveData = FGetData
Exit Function
End If
End If
If GetTickCount - t1 > 2000 Then '2秒没收完就不收了
QReceiveData = ""
Exit Function
End If
Loop
End Function
Private Sub Timer2_Timer()
x1 = x1 + 1
Text10.Text = str(x1)
Text1.Text = str(p11)
Text2.Text = str(p12)
Text3.Text = str(p13)
Text4.Text = str(p14)
Text7.Text = str(p15)
If Text7.Text = 1 Then Text7.BackColor = RGB(255, 0, 255)
If Text7.Text = 0 Then Text7.BackColor = RGB(0, 255, 255)
'Text6.Text = str(p16)
Text9.Text = str(p17)
If Text9.Text = 1 Then Text9.BackColor = RGB(255, 0, 255)
If Text9.Text = 0 Then Text9.BackColor = RGB(0, 255, 255)
'Text8.Text = str(p18)
End Sub