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一直看到有些朋友在問ModBus主從站的通訊問題，今天抽空兒給大家發幾篇。

事先申明，我是調用的主從站庫，庫本身并不是我編寫的，我沒有那么大的能耐。

另外，上位機是用VB編寫，VB本身不是很熟，如果有什么錯誤，請大家海諒。

最后，這僅僅只是一個測試程序，如果各位想用到商業方面，還需要各位自己去完善。

說明：PLC從站，PC作主站，用ModBus協議進行通訊。PC機讀取PLCVW區的數據；PC機還讀取PLC內部I或者O地址的狀態。

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以下是PLC程序實現，方便貼出，已轉換為STL

TITLE=程序注釋

Network 1 // 網絡標題

// 在第一個循環周期內初始化Modbus從站協議

LD SM0.1

CALL SBR3, 1, 12, 9600, 0, 0, 128, 32, 1000, &VB0, M10.1, MB11

Network 2

// 在每個循環周期內執行Modbus 從站協議

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源碼

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 '多項式碼&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) '每一個數據與CRC寄存器進行異或

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 '如果高位字節最后一位為1

CRC16Lo = CRC16Lo Or &H80 '則低位字節右移后前面補1

End If '否則自動補0

If ((SaveLo And &H1) = &H1) Then '如果LSB為1，則與多項式碼進行異或

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 '定時器1無效

Timer1.Interval = 1000 '定時器1時間為1S

Timer2.Enabled = True '定時器2有效

Timer2.Interval = 1000 '定時器2時間為1S

Text1.Text = ""

Text2.Text = ""

Text3.Text = ""

Text4.Text = ""

Text5.Text = ""

Text6.Text = ""

Text8.Text = ""

Text10.Text = ""

MSComm1.CommPort = 1 '設定端口號

MSComm1.Settings = "9600,n,8,1" '設定通訊波特率

MSComm1.InBufferSize = 1024 '接收緩沖器大小

MSComm1.OutBufferSize = 1024 '輸出緩沖器大小

MSComm1.InputMode = comInputModeBinary '以二進制傳輸

MSComm1.RThreshold = 1 '

MSComm1.SThreshold = 0

MSComm1.InputLen = 0 '讀取接收緩沖器所有字符

MSComm1.OutBufferCount = 0 '清空發送緩沖區

MSComm1.InBufferCount = 0 '清空接收緩沖區

If MSComm1.PortOpen = False Then

Command3.Caption = "打開串口"

Else

Command3.Caption = "關閉串口"

End If

End Sub

Private Sub Command1_Click()

Timer1.Enabled = True

End Sub

Private Sub Command2_Click() '退出程序，定時器1無效

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 '打開關閉按鈕顯示文字

Command3.Caption = "關閉串口"

Else

Command3.Caption = "打開串口"

End If

If Err Then '打開串口失敗，則顯示出錯信息

MsgBox Error$, 48, "錯誤信息"

Exit Sub

End If

End Sub

Private Sub Timer1_Timer() '讀V存儲區數據

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 '定義動態數組

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 + he(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 '清空輸出寄存器

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狀態

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 '定義動態數組

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 + he(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 '清空輸出寄存器

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狀態

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 '定義動態數組

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 + he(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 '清空輸出寄存器

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存儲器區數據

Dim FGetData As String

Dim t1 As Long

Dim av As Variant

Dim i As Integer

Dim ReDataLen As Integer

FGetData = ""

t1 = GetTickCount() '取時間，做延時用

Do '循環等待接收數據

DoEvents

If MSComm1.InBufferCount > 0 Then '串口有數據了

ReDataLen = MSComm1.InBufferCount '取數據長度

av = MSComm1.Input '將串口數據取出來

For i = 0 To ReDataLen - 1

FGetData = FGetData & Right("00" & he(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秒沒收完就不收了

ReceiveData = ""

Exit Function

End If

Loop

End Function

Private Function IReceiveData() As String '反回I狀態

Dim FGetData As String

Dim t1 As Long

Dim av As Variant

Dim i As Integer

Dim ReDataLen As Integer

FGetData = ""

t1 = GetTickCount() '取時間，做延時用

Do '循環等待接收數據

DoEvents

If MSComm1.InBufferCount > 0 Then '串口有數據了

ReDataLen = MSComm1.InBufferCount '取數據長度

av = MSComm1.Input '將串口數據取出來

For i = 0 To ReDataLen - 1

FGetData = FGetData & Right("00" & he(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秒沒收完就不收了

IReceiveData = ""

Exit Function

End If

Loop

End Function

Private Function QReceiveData() As String '反回Q狀態

Dim FGetData As String

Dim t1 As Long

Dim av As Variant

Dim i As Integer

Dim ReDataLen As Integer

FGetData = ""

t1 = GetTickCount() '取時間，做延時用

Do '循環等待接收數據

DoEvents

If MSComm1.InBufferCount > 0 Then '串口有數據了

ReDataLen = MSComm1.InBufferCount '取數據長度

av = MSComm1.Input '將串口數據取出來

For i = 0 To ReDataLen - 1

FGetData = FGetData & Right("00" & he(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秒沒收完就不收了

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