Tag Archives: modbus rtu

Productivity 1000 Series PLC Modbus RTU Serial Communication

The productivity series of PLCs comes with 4 built-in communication ports for easy connectivity to your PC or various industrial networks. Serial protocols like Modbus RTU can be utilized with either the RS232 or RS485 ports on this PLC. Modbus RTU is an open (published) protocol that uses the Master / Slave architecture. It’s a very common protocol used in industrial automation controls.

We will be using the RS485 (2-wire) port to communicate to a Solo Process Temperature Controller. Modbus RTU will be the protocol used on this serial communication media. The PLC will be the master and the Solo process temperature controller will be the slave. You will soon see how the Productivity Series of PLC’s is the best way to handle communication to other devices. Let’s get started. Continue Reading!

BRX PLC Serial Communication – Modbus RTU to Solo Process Temperature Controller

Serial communication instructions will allow you to send and receive serial data to an external device. The communication method that you setup can be ASCII or numeric (binary). ASCII (American Standard Communication for Information Interchange) can be used to send to devices such as a printer or display.

Receiving ASCII can be used for connecting barcode scanners to the PLC. The barcode will be read as an ASCII string in the PLC.

The BRX Series PLC will allow you to use instructions such as STREAMIN and STREAMOUT to send and receive data from devices mentioned above. They are usually a one to one device and do not have a protocol.
A protocol is like a language used to communicate to different devices connected together. Modbus serial communication (Modbus RTU) is a standard protocol used in many industrial automation devices. The BRX Series PLC has a MRX (Modbus Network Read) and MWX (Modbus Network Write) instructions.

We will demonstrate these instructions by communicating Modbus RTU to a Solo Temperature Controller. (RS485) Our example will read the current process (PV) value and write the set point value (SV) in the controller. Let’s get started. Continue Reading!

Modbus RTU BRX PLC Master to Click PLC Slave Communication

Recently I was asked to demonstrate communication between a BRX PLC and Click PLC using Modbus RTU. Both PLCs are available from automation direct com. Modbus serial communication (Modbus RTU) is a standard protocol used in many automation devices. It works on a Master / Slave configuration. You can have only one master per network on Modbus RTU (Remote Terminal Unit). A maximum of 32 devices (Nodes) on the network can communicate to the master. A review of the Modbus RTU protocol (RTU frames) can be seen at the following URL.
http://www.rtaautomation.com/technologies/modbus-rtu/
Using the BRX PLC as a Master, we will be communicating to the Click PLC (Slave). Our example will read 10 registers from the Click PLC and write 10 registers from the BRX PLC. Let’s get started! Continue Reading!

AdvancedHMI to Solo Process Temperature Controller

Modbus RTU will be the serial (RS485) method in which we will communicate between the AdvancedHMI Screen and the Automation Direct Solo Process Temperature Controller.
We can address up to 247 (Solo 1 to 247) devices on this master – slave protocol. A maximum of 32 devices (Nodes) on the network can communicate to the master. A review of the Modbus RTU protocol can be seen at the following URL.
http://www.rtaautomation.com/technologies/modbus-rtu/

AdvancedHMI is a free HMI programming package the runs on Microsoft Visual Studio. It can be downloaded at the following URL.
https://sourceforge.net/projects/advancedhmi/

Connections:
We will be running the AdvancedHMI software on the computer. One of the USB ports will have an USB to RS485 adapter and communicate RS485 to the Solo process temperature controller.
Solo Process Temp Controller 010 Communication Diagram-min
See the following post to install the USB to RS485 adapter.
https://accautomation.ca/usb-to-rs485-pc-adapter-installation/

Solo Controller Settings:
In the Initial Setting Mode we will change the on line configuration to on and make the changes to the Modbus settings as follows: 9600 Baud, Even, 7 Data Bits, 1 Stop Bit, Modbus ASCII Format. We will leave the default unit number as 1. See the following post to set the controller:
https://accautomation.ca/solo-process-temperature-controller/

Modbus RTU (Addresses)
The following address will be used in our project:
AdvancedHMI to Solo 050-min

AdvancedHMI to Solo 055-min
AdvancedHMI will use the Modbus Decimal value in the PLCAddressValue to determine the information that you want to get. For a list of all Modbus addresses that can be used in your project, refer to the Solo Manual located a the following URL:
https://www.automationdirect.com/adc/Manuals/Catalog/Process_Control_-a-_Measurement/Temperature_-z-_Process_Controllers

Screen Display: (AdvancedHMI)
Here is what our screen will look like:
AdvancedHMI to Solo 010-min
We have mimicked the look of the solo process temperature controller. Our PV and SV values are DigitalPanelMeters from the AdvancedHMI toolbar.  The eight output indicators are just labels.

Our ModbusRTUCom1 settings are as follows:
AdvancedHMI to Solo 030-min
Settings: 9600, 8, Even, One StopBit and Station 1 should all match the settings in the Solo process temperature controller that we did previously.
PollRateOverride will allow us to determine how often the communication will take place to the controller. (250msec)
The PortName will be the same port number that the computer will communicate out of. This will be set when you install the USB to RS485 adapter. It may change if a different USB port is used.

The DataSubsciber1 will be used to determine the status of the controller.
AdvancedHMI to Solo 040-min
PLCAddressValue = 44139

We read the value of the eight status bits and convert this into a string so we can determine the status of each of the individual bits. Here is the code that is used to do this. It is the only code required for this application.

Private Sub DataSubscriber1_DataChanged(sender As Object, e AsDrivers.Common.PlcComEventArgs) Handles DataSubscriber1.DataChanged
        Dim i As Integer = DataSubscriber1.Value
        Dim Status As String
        Status = Convert.ToString(i, 2).PadLeft(8, "0") '8 bits
        'There are 8 bits that we need to check and account for on our screen. 
        'Modbus Decimal - 44139
        'Bit 0 - ALM3 - Alarm 3
        'Bit 1 - ALM2 - Alarm 2
        'Bit 2 - C degrees
        'Bit 3 - F degrees
        'Bit 4 - ALM1 - Alarm 1
        'Bit 5 - OUT 2 
        'Bit 6 - OUT 1
        'Bit 7 - AT - Auto Tuning

The complete AdvancedHMI code for this application can be downloaded at the end of the post.

The PV and SV indicators are DigitalPanelMeters as mentioned above.
AdvancedHMI to Solo 060-min

AdvancedHMI to Solo 065-min
They both have four digits with a decimal position of 1. This will give us a value between 000.0 and 999.9.
The SV includes a keypad to change the set value. KeypadScaleFactor is set to 0.1 to allow for the decimal place.

Included in our display is a BasicTrendChart from the AdvancedHMI toolbar.
AdvancedHMI to Solo 075-min

AdvancedHMI to Solo 070-min
You want to make sure that the YMaximum and YMinimum settings are set so the values will not go past these settings. If they do then the graph line will disappear from the chart at that point and time.
This will show a running trend for the last 5 minutes.
Polling rate is 250msec x 1200 points in the chart = 300 000msec
300 000msec / 1000 = 300 seconds
300 seconds / 60 (seconds in minute) = 5 minutes

Notes: Displaying Extended ASCII Symbols in Visual Studio (VB.NET)
You can display any symbol in the visual studio environment by holding the ‘Alt’ key down and typing the decimal number of the symbol that you want. In our example the degrees symbol is Alt 248.
Here are the extended ASCII symbols:
AdvancedHMI to Solo 020-min
http://www.asciitable.com/

Running the Application:
AdvancedHMI to Solo 085-min

You will notice that the response rate is very quick. (250msec) As the PV, SV or indication values change, the screen will get updated.AdvancedHMI to Solo 090-min

The trend chart will show the last 5 minutes of the PV value. AdvancedHMI to Solo 095-min

As you can see, programming the AdvancedHMI to communicate to the Solo process temperature controller is very easily done.

Download the AdvancedHMI code for this project here.

Watch on YouTube : AdvancedHMI to Solo Process Temperature Controller
If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.




USB to RS485 PC Adapter Installation

The USB-485M is a 2-wire USB to RS-485 serial communication adapter for RS485 use. It does not require an external power supply or complicated configuration.

It has a Type A (plug) USB connector for the computer side and a universal female RJ45/RJ12 modular connector. This will accept RJ12 and RJ45 plugs.  The USB-485M supports multiple baud rates and is USB V2.0 Compliant.

Installing the Driver
Do NOT connect the USB-485M to your PC before installing the driver file.

Go to the Automation Direct website and download the latest drivers for this device. I would not use the mini CD that came with the converter because it may be out of date.
USB-485M Serial Converter Support Resources
USB RS485 Installation 010-min

Download and extracted the zip file. (Right click on the zip file and select Extract All…. )
If you have a 64bit computer double click on the following file:
CP210xVCPInstaller_x64.exe
If you have a 32bit computer double click on this file:
CP210xVCPInstaller_x86.exe

If you are unsure as to 32 bit or 64 bit computer then go to control panel and look under system. Under System type it will display either a 32-bit Operating or 64-bit Operating system.
Alternatively on Windows 7 you can click start and right click on Computer.
USB RS485 Installation 080-min
Selecting properties will call up the system information for you.
USB RS485 Installation 090-min

This will now start the installation of the CP210x USB to UART Bridge Driver. Select Next.USB RS485 Installation 020-min

You must accept the license agreement before the software will install. Select ‘I accept this agreement’ and hit Next.USB RS485 Installation 030-min

You will now get a message that the installation is complete. The Silicon Laboratories Driver is now installed. Click Finish.USB RS485 Installation 040-min

We will now configure the device driver for our hardware.
Connect the USB-485M to your PC.
The driver software installation will begin by searching for the CP2103 USB to UART Bridge Controller. It will start by searching windows update…
USB RS485 Installation 050-min

Once the software has been configured a message will be displayed as follows. If it cannot find the driver software you can manually select the x64 (64bit) or x86 (32bit) folders from the downloaded driver files.USB RS485 Installation 060-min

You can now call up device manager and view the ports on your computer. The Silicon Labs CP210x USB to UART Bridge is on communication port 5. USB RS485 Installation 070-min

We are now ready to connect to our equipment. Since this is a serial device and is a 1 : N connection. This means that we will have a master and at least one slave unit. All communication must have the same parameters when communicating. What separates the communication is that each slave is assigned an unique number.
Example:

Device Computer ‘Master’ Solo Process Controller
‘Slave’
Do-More PLC
‘Slave’
Additional Devices
‘Slaves’
Station Address / Unit number N/A 1 2
Baud Rate 9600 9600 9600 9600
Data Bits 8 8 8 8
Parity Even Even Even Even
Stop Bits 1 1 1 1

Protocol is the actual communication (Information format that is transferred) that takes place over the network. (Master to Slaves)

Watch on YouTube : USB to RS485 PC Adapter Installation
If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.




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



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.