Siemens S7-200 ModBus slave communication program - Database & Sql Blog Articles

Photocoupler

I have been seeing some friends asking about the communication problems of the ModBus master and slave stations. I took the time to send you a few articles today.

I declare in advance that I am calling the master slave library. The library itself is not written by me. I am not as capable.

In addition, the host computer is written in VB, VB itself is not very familiar, if there is any error, please forgive me.

In the end, this is just a test procedure. If you want to use the business side, you need to improve it yourself.

Description: The plc slave station, the PC as the master station, communicates with the ModBus protocol. The PC reads the data of the PLCVW area; the PC also reads the status of the internal I or O address of the PLC.

////////////////////////////////////////////

The following is a PLC program implementation, easy to post, has been converted to STL

TITLE=Program Notes

Network 1 // Network title

// Initialize the Modbus slave protocol in the first cycle

LD SM0.1

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

Network 2

// Execute the Modbus Slave Protocol in each cycle

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

///////////////////////////////////////

The following is the VB source code

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 Register

Dim CL As Byte, CH As Byte "Polynomial Code & 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) "Each data is XORed with the CRC register

For Flag = 0 To 7

SaveHi = CRC16Hi

SaveLo = CRC16Lo

CRC16Hi = CRC16Hi \ 2 "High bit right shift one bit

CRC16Lo = CRC16Lo \ 2 "Low right shift one bit

If ((SaveHi And &H1) = &H1) Then "If the last bit of the high byte is 1

CRC16Lo = CRC16Lo Or &H80 "The lower byte is shifted right after the first 1

End If "other automatically fills 0

If ((SaveLo And &H1) = &H1) Then "If the LSB is 1, then XOR with the polynomial code

CRC16Hi = CRC16Hi Xor CH

CRC16Lo = CRC16Lo Xor CL

End If

Next Flag

Next i

Dim ReturnData(1) As Byte

ReturnData(0) = CRC16Hi "CRC high

ReturnData(1) = CRC16Lo "CRC low"

CRC16 = ReturnData

End Function

Private Sub About_Click()

frmAbout.Show

End Sub

Private Sub Form_Load() "Initialization

Timer1.Enabled = False "Timer 1 is invalid

Timer1.Interval = 1000 "Timer 1 time is 1S

Timer2.Enabled = True "Timer 2 is valid

Timer2.Interval = 1000 "Timer 2 time is 1S

Text1.Text = ""

Text2.Text = ""

Text3.Text = ""

Text4.Text = ""

Text5.Text = ""

Text6.Text = ""

Text8.Text = ""

Text10.Text = ""

MSComm1.CommPort = 1 "Set the port number

MSComm1.Settings = "9600,n,8,1" "Set communication baud rate

MSComm1.InBufferSize = 1024 "receive buffer size

MSComm1.OutBufferSize = 1024 "Output buffer size

MSComm1.InputMode = comInputModeBinary "Transfer in binary

MSComm1.RThreshold = 1 "

MSComm1.SThreshold = 0

MSComm1.InputLen = 0 "Read all characters of the receive buffer

MSComm1.OutBufferCount = 0 "Empty send buffer

MSComm1.InBufferCount = 0 "Empty receive buffer

If MSComm1.PortOpen = False Then

Command3.Caption = "Open Serial Port"

Else

Command3.Caption = "Close Serial Port"

End If

End Sub

Private Sub Command1_Click()

Timer1.Enabled = True

End Sub

Private Sub Command2_Click() "Exit program, timer 1 is invalid

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 "Open the close button to display text

Command3.Caption = "Close Serial Port"

Else

Command3.Caption = "Open Serial Port"

End If

If Err Then "Failed to open the serial port, an error message is displayed.

MsgBox Error$, 48, "Error Message"

Exit Sub

End If

End Sub

Private Sub Timer1_Timer() "Read V memory area data

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 "Define dynamic arrays

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 "Empty output register

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 state

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 "Define dynamic arrays

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 "Empty output register

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 Status

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 "Define dynamic arrays

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 "Empty output register

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 "Returns V memory area data

Dim FGetData As String

Dim t1 As Long

Dim av As Variant

Dim i As Integer

Dim ReDataLen As Integer

FGetData = ""

T1 = GetTickCount() "take time, do delay

Do "loop waiting to receive data

DoEvents

If MSComm1.InBufferCount > 0 Then "The serial port has data.

ReDataLen = MSComm1.InBufferCount "Get data length

Av = MSComm1.Input "Remove serial data

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 seconds after the harvest is over, it will not be received.

ReceiveData = ""

Exit Function

End If

Loop

End Function

Private Function IReceiveData() As String "Reverse I state

Dim FGetData As String

Dim t1 As Long

Dim av As Variant

Dim i As Integer

Dim ReDataLen As Integer

FGetData = ""

T1 = GetTickCount() "take time, do delay

Do "loop waiting to receive data

DoEvents

If MSComm1.InBufferCount > 0 Then "The serial port has data.

ReDataLen = MSComm1.InBufferCount "Get data length

Av = MSComm1.Input "Remove serial data

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 seconds after the harvest is over, it will not be received.

IReceiveData = ""

Exit Function

End If

Loop

End Function

Private Function QReceiveData() As String "Reverse Q state"

Dim FGetData As String

Dim t1 As Long

Dim av As Variant

Dim i As Integer

Dim ReDataLen As Integer

FGetData = ""

T1 = GetTickCount() "take time, do delay

Do "loop waiting to receive data

DoEvents

If MSComm1.InBufferCount > 0 Then "The serial port has data.

ReDataLen = MSComm1.InBufferCount "Get data length

Av = MSComm1.Input "Remove serial data

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 seconds after the harvest is over, it will not be received.

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