How to Implement Modbus TCP Protocol using VBA with Excel

We will use Visual Basic for Applications (VBA) to communicate to a PLC using Modbus TCP protocol. Reading ten registers in the PLC and displaying a bar graph in Excel. Previously we have used VB6 to communicate Modbus TCP.
The following steps will be done:

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

 

The Modbus TCP/IP or Modbus TCP is a Protocol  that is used for communications over TCP/IP networks. This is done on port 502. Modbus TCP does not require a checksum calculation as lower layers already 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

 

OstroSoft Winsock Component
OSWINSCK.dll serves as a wrapper for the Winsock API and helps programmers to abstract from the complexity of API calls and focus on application functionality. Works with programming and scripting languages supporting COM.
You will need to 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 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 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’Modbus TCP using VBA Excel 022-minCheck 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. Modbus TCP using VBA Excel 040-min
From the menu – Tools | References
We can now add the OstroSoft Winsock Component to our application.
Select OK
Modbus TCP using VBA Excel 050-minSelect Sheet1(Sheet1). Modbus TCP using VBA Excel 060-min

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

‘This example uses OstroSoft Winsock Component
‘http://www.ostrosoft.com/oswinsck.asp

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
 
  DoEvents
  nPort = 502 ‘ See configuration in Do-More Designer
  ‘ Set the IP address of the PLC
  sServer = Sheets(“Sheet1”).Range(“B4″) ‘”192.168.1.3”
  RetrieveData = 1
  CommandButton1.BackColor = “&H0000FF00” ‘ Set colour 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 remote host name
‘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 occured

‘ If TCP is not connected, try to connect again.
If wsTCP.State <> 7 Then
    If (wsTCP.State <> sckClosed) Then
      wsTCP.CloseWinsock
    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))
        DoEvents
    Loop
    If (wsTCP.State = 7) Then
    Else
       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
    ‘0002:    The number of registers to write
   
    ‘ 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

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

DoEvents
‘ 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

Interface:
Go back to Sheet1 and we can now put on the worksheet what we would like to see.

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

Modbus TCP using VBA Excel 070-min

 

Communication to the PLC

Start the Do-More Designer software.
Under the Project Browser select ‘System Configuration’
Modbus TCP using VBA Excel 125-min
Make 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 in the range 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 gets to the value above 4000, a move instruction will put a 0 back into MHR 1.
If input X0 turns on then the value in XW0 will be moved into MHR1 and the previous clock bit will not be in effect. Values will be between 0 and 4096. (12 bit resolution)
Modbus TCP using VBA Excel 150-min

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

Running the program will produce the following:Modbus TCP using VBA Excel 120-min

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 contact me.
Thank you,
Garry



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21 thoughts on “How to Implement Modbus TCP Protocol using VBA with Excel”

    1. I am not sure of the question that you are asking. What Modbus device are you connected to? (What are the settings of that device?)
      What function code/s are you using?
      Regards,
      Garry

      1. Hi Luca,
        In the Modbus protocol we specify the address and the number of registers to read. 32 bit addresses will be twice as long as 16. We would just specify the starting address and twice the amount of registers to read. Take the result and join them together.

            ‘ 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
            ‘0002:    The number of registers to read

        Regards,
        Garry

  1. Great tutorial!

    Reading the addresses with the Excel file works perfect. I do however get the error “10053: Software caused connection abort.” after some time when i click the Stop Data button.

    Does the oswin socket have a timer that closes the connection when it is not used for some time? (meaning I should close the handler when i stop the data acc.)

    1. Hi Christian,
      You are correct. The oswinsck must be closed. I did forget to include this in the sample program.
      I would enter another timer that gets activated when the connection is closed.
      If (wsTCP.State <> sckClosed) Then
      wsTCP.CloseWinsock
      End If
      Thanks Christian,
      Garry

      1. Garry,
        I am getting “Compile error: Variable not defined”. In the code, “” is highlighted withing the line:
        returninfo = “”

        I am aslwo using Windows 7, Excel 2010.

        Any thoughts?

        Thank you,
        Justin

          1. Here are those few lines (copy and pasted):

            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))

          2. Hi Justin,
            Here are the exact same lines copied and pasted below. Note the spelling of returnInfo not returninfo. If you keep the returninfo spelling then go back and change the following line of code:
            Dim returnInfo change to Dim returninfor

            returnInfo = “”
            For i = 1 To bytesTotal
            wsTCP.GetData j, vbByte
            MbusByteArray(i) = Asc(Mid(sBuffer, i, 2))
            returnInfo = returnInfo & Asc(Mid(sBuffer, i, 2))
            Next
            txtSource = returnInfo

  2. Hi Sir
    ACC Modbus TCP Connect Excel VBA with LS Industrial Systems (XGB_XBC) PLC
    We tested communication.
    It shows the following result values

    PLC value 1 ~ 128 -> Excel 1 ~ 128 The normal value is displayed
    PLC value 129 ~ 254 -> Excel 63 Only certain values are displayed
    PLC value 255 ~ 384 -> Excel 255 ~ 384 The normal value is displayed
    PLC values 385 to 510 -> Excel 319 Only certain values are displayed
    PLC value 511 to 640 -> Excel 511 to 640 The normal value is displayed
    PLC values 641 to 766 -> Excel 575 Only certain values are displayed

    Tell me what’s wrong with this pattern in Excel
    Thank you

    수정 제안하기

    1. Hi Ji
      Since information is being received in Excel, then all communication is working correctly. I would look at the address registers in the PLC to determine the register type (Binary, Hex, ASCII, Decimal, etc).
      See if there is a relationship between the register type and the information being returned in Excel.
      Regards,
      Garry

        1. Hi Ji,
          I provide this information free of charge to you. There is nothing to purchase. The advertising that you see on the website and videos help to pay for the upkeep of the site.
          This is my way of giving back to our automation field.
          Regards,
          Garry

  3. Can we use same VBA script for modbus RTU (serial) device over which is connected to TCPIP ethernet converter ?

    If yes then where we will put device ID, baud rate, parity, stop bit in your excel file and VBA script ?

    1. Hi Santosh,
      Yes you can use VBA script to communicate through the serial port Modbus RTU. Here is a link where you will find additional information.
      https://pps2.com/smf/index.php?topic=25.0
      You would specify the serial communications when opening the serial port. The device ID would be similar to the Modbus TCP example above.
      Hope this helps you out.
      Regards,
      Garry

  4. Hi There,

    I really like this spread sheet you made but I cannot get it to work. I am trying to read 400001-400008 on a productivity 2000 plc. I have those locations setup as 32 bit integers but I could change that. Any differences between the two PLCs that could cause this not to work?

    1. Hi Jordan,
      Once the Mod Start and Mod End are set up in the Productivity Suite software. These addresses should be able to read.
      Are you able to program through the Ethernet port of the controller? This will prove that the cable is correct.
      Modbus Server Settings can be seen from the productivity suite software. ( File | Project Properties ) Under the tab Modbus Server Settings you will see a series of options. I usually keep this as the default.
      If everything else fails you can try another Modbus Client like AdvancedHMI. This will prove the communications to the PLC.
      https://sourceforge.net/projects/advancedhmi/
      Here is a post on installing this software:
      http://accautomation.ca/create-a-plc-with-hmi-training-and-learning-environment-free/

      Regards,
      Garry

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