How to Implement Modbus TCP Protocol VBA Excel

We are using Modbus TCP protocol, reading ten registers in the PLC, and displaying a bar graph in Excel. e will use Visual Basic for Applications (VBA) to communicate with a PLC. Previously we have used VB6 to communicate Modbus TCP.

Sequence for Modbus TCP on Excel using VBA

The following steps will be done:

  1. Explain the Modbus TCP protocol
  2. Install OstroSoft Winsock Component
    – Winsock API Calls for communication on the network
  3. Develop the Excel and VBA application
    (Microsoft Excel 2010)
  4. Communicate to the PLC and sample code
    (Do-More Simulator)


What is Modbus TCP (Ethernet)

The Modbus TCP/IP or Modbus TCP is a protocol for communications over TCP/IP networks. This is done on port 502. Modbus TCP does not require a checksum calculation as lower layers provide checksum protection. You can think of this as a letter being sent, and Ethernet TCP/IP acts like an envelope for the Modbus Commands. I will not go into the details of the communication protocol, but here are some links to references:
Introduction to Modbus TCP/IP
Simply Modbus – Modbus TCP

Winsock Component – Excel VBA Modbus TCP

OstroSoft Winsock Component
OSWINSCK.dll is a wrapper for the Winsock API and helps programmers abstract from the complexity of API calls and focus on application functionality. Works with programming and scripting languages supporting COM.
You must download and install the OstroSoft Winsock Component on your computer.
For use with .NET, Visual Basic 4 or 5, Visual C++, ASP, VBA, VBScript, JavaScript, or any other language, supporting COM:
1. Download oswinsck.exe
Modbus TCP using VBA Excel 001-min

2. Run the downloaded file from Windows Explorer or command-line
Modbus TCP using VBA Excel 002-min
Hit OK
Modbus TCP using VBA Excel 003-min
I use the default directories where the program will be installed. Click the button to install.
Modbus TCP using VBA Excel 004-min
Leave the program group to the default, so I know what the program is after installation. Click continue.
Modbus TCP using VBA Excel 005-min
Click OK
The OstroSoft Winsock Component is now installed.

Start Microsoft Excel

Modbus TCP using VBA Excel 010-min
Select ‘Developer’ along with the top tabs.
Modbus TCP using VBA Excel 020-min

If the Developer tab is not present, then we must turn on the developer tab.
Select File | Options Modbus TCP using VBA Excel 021-minSelect ‘Customize Ribbon’Check the ‘Developer’ under Main Tabs. Modbus TCP using VBA Excel 023-min

Under the Developer menu. Select ‘Visual Basic’
Modbus TCP using VBA Excel 030-minThe Visual Basic Editor window will now be displayed. Ethernet visual basic assistance communication
From the menu – Tools | References
We can now add the OstroSoft Winsock Component to our application.
Select OK
Ethernet visual basic assistance communicationSelect Sheet1(Sheet1). Ethernet visual basic assistance communication

Visual Basic Code – Excel VBA for Modbus TCP

Now put the visual basic code in Sheet1(Sheet1)
Here is the code:

‘This example uses OstroSoft Winsock Component

Option Explicit

Dim bytesTotal As Long
Dim sPage As String
Dim MbusQuery
Dim returnInfo
Dim wsTCPgdb
Dim WithEvents wsTCP As OSWINSCK.Winsock
Dim SetObject
Dim RetrieveData

Private Sub CommandButton1_Click() ‘ Retrieve Data
On Error GoTo ErrHandler
  Dim sServer As String
  Dim nPort As Long
  Dim StartTime
  nPort = 502 ‘See configuration in Do-More Designer
  ‘Set the IP address of the PLC
  sServer = Sheets(“Sheet1”).Range(“B4″) ‘””
  RetrieveData = 1
  CommandButton1.BackColor = “&H0000FF00” ‘Set a color to Green

‘Check to see if the object has been created. If not set wsTCP.
If SetObject = “” Then
Set wsTCP = CreateObject(“OSWINSCK.Winsock”)
wsTCP.Protocol = sckTCPProtocol
SetObject = 1
  End If

‘Check the state of the TCP connection
‘0 sckClosed connection closed
‘1 sckOpen open
‘2 sckListening listening for incoming connections
‘3 sckConnectionPending connection pending
‘4 sckResolvingHost resolving the remote hostname
‘5 sckHostResolved remote host name successfully resolved
‘6 sckConnecting connecting to remote host
‘7 sckConnected connected to remote host
‘8 sckClosing Connection Is closing
‘9 sckError error occurred

‘If TCP is not connected, try to connect again.
If wsTCP.State <> 7 Then
    If (wsTCP.State <> sckClosed) Then
    End If
    ‘Open the connection
    wsTCP.Connect sServer, nPort
    StartTime = Timer’ Use the timer to determine if a connection cannot be made
    Do While ((Timer < StartTime + 2) And (wsTCP.State <> 7))
    If (wsTCP.State = 7) Then
       Exit Sub
    End If
End If

‘If we are connected, then request the information.
If (wsTCP.State = 7) Then
    MbusQuery = Chr(0) + Chr(0) + Chr(0) + Chr(0) + Chr(0) + Chr(6) + Chr(0) + Chr(3) + Chr(0) + Chr(0) + Chr(0) + Chr(20)
    wsTCP.SendData MbusQuery ‘Send out the Modbus Information
    ‘Read the information
    ‘0000:    Transaction Identifier
    ‘0000:    Protocol Identifier
    ‘0006:    Message Length (6 bytes to follow)
    ’00:      The Unit Identifier
    ’03:      The Function Code (read MHR Read Holding Registers)
    ‘0000:    The Data Address of the first register
    ‘0020:    The number of bytes to read
    ‘Write the information
    ‘0000:    Transaction Identifier
    ‘0000:    Protocol Identifier
    ‘0009:    Message Length (6 bytes to follow)
    ’01:      The Unit Identifier
    ’16:      The Function Code (read Analog Output Holding Registers)
    ‘0000:    The Data Address of the first register
    ‘0001:    The number of registers to write
    ’02:      The number of data bytes to follow
    ‘0030     The number to put into the register
    ‘Note: Addresses are offset by 1
    ‘   Example: MHR1 = Address 0000
    ‘   Example: MHR30 = Address 0029
End If
  Exit Sub

  MsgBox “Error ” & Err.Number & “:” & Err.Description
End Sub
Private Sub CommandButton2_Click() ‘ Stop the communication
RetrieveData = 0
CommandButton1.BackColor = “&H8000000F”‘ Set the default color
End Sub

Private Sub wsTCP_OnDataArrival(ByVal bytesTotal As Long)
  Dim sBuffer
  Dim i
  Dim MbusByteArray(500)
  Dim h As Integer
  Dim txtSource
wsTCP.GetData sBuffer
  txtSource = txtSource & sBuffer
Dim j As Byte
returnInfo = “”
For i = 1 To bytesTotal
    wsTCP.GetData j, vbByte
    MbusByteArray(i) = Asc(Mid(sBuffer, i, 2))
    returnInfo = returnInfo & Asc(Mid(sBuffer, i, 2))
 txtSource = returnInfo
 txtSource = Val(Str((MbusByteArray(10) * 256) + MbusByteArray(11)))
 Sheets(“Sheet1”).Range(“B10”) = Val(Str((MbusByteArray(10) * 256) + MbusByteArray(11)))
 Sheets(“Sheet1”).Range(“B11”) = Val(Str((MbusByteArray(12) * 256) + MbusByteArray(13)))
 Sheets(“Sheet1”).Range(“B12”) = Val(Str((MbusByteArray(14) * 256) + MbusByteArray(15)))
 Sheets(“Sheet1”).Range(“B13”) = Val(Str((MbusByteArray(16) * 256) + MbusByteArray(17)))
 Sheets(“Sheet1”).Range(“B14”) = Val(Str((MbusByteArray(18) * 256) + MbusByteArray(19)))
 Sheets(“Sheet1”).Range(“B15”) = Val(Str((MbusByteArray(20) * 256) + MbusByteArray(21)))
 Sheets(“Sheet1”).Range(“B16”) = Val(Str((MbusByteArray(22) * 256) + MbusByteArray(23)))
 Sheets(“Sheet1”).Range(“B17”) = Val(Str((MbusByteArray(24) * 256) + MbusByteArray(25)))
 Sheets(“Sheet1”).Range(“B18”) = Val(Str((MbusByteArray(26) * 256) + MbusByteArray(27)))
 Sheets(“Sheet1”).Range(“B19”) = Val(Str((MbusByteArray(28) * 256) + MbusByteArray(29)))

‘Determine if we retrieve the data again.
If RetrieveData = 1 Then
    Call CommandButton1_Click
End If
End Sub

Private Sub wsTCP_OnError(ByVal Number As Integer, Description As String, ByVal Scode As Long, ByVal Source As String, ByVal HelpFile As String, ByVal HelpContext As Long, CancelDisplay As Boolean)
  MsgBox Number & “: ” & Description
End Sub

Private Sub wsTCP_OnStatusChanged(ByVal Status As String)
  Debug.Print Status
End Sub

Note: The program utilizes the CHR and STR functions to convert the data from binary to ASCII and back.
The highest value of a byte of data is 256. This is why we have to multiply the highest significant byte with 256

Go back to Sheet1, and we can now put what we want to see on the worksheet.

Note the following:
IP Address = B4
MHR 1 to 10 values located at B10 to B19
‘Stop Data’ – CommandButton2
‘Retrieve Data’ – CommandButton1

Ethernet visual basic assistance communication


Communication with the PLC

Start the Do-More Designer software.
Under the Project Browser, select ‘System Configuration.’
Ethernet visual basic assistance communication
Make a note of the IP address. If you are running the simulator, then this is automatically filled in.
Modbus TCP using VBA Excel 126-min
Ensure that the Enable Modbus/TCP Server is checked. Also, make sure that the TCP Port Number is 502.
Modbus TCP using VBA Excel 127-min

The sample PLC program will write values from 0 to 4000. These values will be put in MHR 1 to MHR 10.

Here is the first couple of rungs of the PLC program. It will use clock bit flags to increment the MHR 1 channel. When it reaches a value above 4000, a move instruction will put a 0 back into MHR 1.
If input X0 turns on, the value in XW0 will be moved into MHR1, and the previous clock bit will not be in effect. Discounts will be between 0 and 4096. (12-bit resolution)
Ethernet visual basic assistance communication

This is repeated with different internal clock bit flags up to MHR10.

Running the program will produce the following:
Ethernet visual basic assistance communication

As you can see, the Modbus TCP protocol is easy to implement with visual basic for applications.
Download the PLC program and Excel file.

Additional Information:
Excel – Conditional Movement of Data

Watch on YouTube: How to Implement Modbus TCP Protocol using VBA with Excel

If you have any questions or need further information, please get in touch with me.
Thank you,

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