Previously we used VB6 (Visual Basic 6) to implement the Omron Host Link Protocol to communicate to our programmable logic controller. (PLC) In part 2 we used Visual Basic for Applications (VBA) to accomplish our host link serial communication. We will now look at using VB.Net to establish and retrieve information in and out of the PLC using host link. (C mode commands)
Hostlink communication protocol is a method developed by Omron for communication to PLC’s and other equipment. This ASCII based protocol is used over RS232 or RS422/RS485. It is a many to one implementation which means that you can communicate with up to 32 devices back to a master. (1:N) This communication on the industrial floor can control PLC’s, Temperature Controllers, Panel Meters, etc.
The Omron CP1H plc will be used with a CP1W-CIF11 (RS485) communication serial link adapter. We will also use a USB-485M Universal Serial Bus to RS485 adapter from automation direct. The video at the end of this post will demonstrate the communications by reading 10 registers form the DM area of the PLC. Continue Reading!
Utilizing the CX Server DDE Manager will allow us to provide a link to the information in the Omron PLC. This link can be placed on an Excel spreadsheet. Charts, graphs, etc. can be made from the data. We will create links on an excel spread sheet from a CQM1H and a CP1L PLC. The information will then be displayed as a bar graph comparing the first ten memory areas.
Dynamic Data Exchange (DDE) is a channel through which correctly prepared programs can actively exchange data and control other applications within Microsoft Windows. The DDE manager will allow us to set up all of the links.
Start the DDE Manager by clicking Start/Programs/Omron/CX-Server/DDE Manager
This will start the DDE Manager and place an icon on your toolbar at the bottom of your screen. The application will run minimized.
Right-click on the minimized DDE Manager icon and select Project/New.
Assign a filename (ACC DDE.cdm) to the CX-Server project that you will create, and save it.
The create project will minimize to the taskbar. Right-click on the minimized DDE Manager icon and select Project/Edit.
This will call up the DDE Manager Project Editor. We can now add the PLC’s (Devices) and Points that we want to display.
Select File/New/PLC, or hit the PLC Icon on the taskbar.
Under Change PLC, we can now enter the information about how we are communicating to the programmable logic controller.
Device Name: – Name in which the DDE Manager will call the PLC
Device Type: – The model of PLC that will be connected
Network Type: – This is the communication method that we will be talking with the device.
In our example we will use the following two Omron PLCs.
CQM1H – SYSMAC WAY (Omron Host Link Protocol) Communication Port 11, 9600, E, 7, 2. Unit #00
CP1L – USB
Once we have the PLC information, we can now add points that will contain the information that we wish to retrieve from the units. Select File/New/Point or select the point editor icon to start the point editor.
On the Logical tab you can give a name (Or Change) to the point in the PLC to get. Select the Physical tab.
On the physical tab we set the following information: PLC: – This is the list of PLCs entered in the previous step Data Location: – The memory location that we want to read from Internal Data Type: – This is the interpretation of the data that we are reading. (Example: Bit, Word, BCD, etc.) Command Modifier: – This is used if we need to Force Set / Reset the data location. This can be used to override the PLC program. Use with caution.
Press OK when finished setting the address.
Our point is now programmed. You will notice the symbols before the name of the point. This tells us at a quick glance what type of data we are looking at. Please refer to the CX Server Runtime manual for all of the symbol meanings.
Fill out the remaining points for our example.
CP1L – D0 to D9
CQM1H – DM0 to DM9
Start Microsoft Excel.
Go back to the DDE manager and the points under the Project Editor. We can now select the first ten items in the list. Click the first one and then move to the last item. Hold the shift while clicking the last item will select all of them between.
Hit the DDE Link icon.
In Excel, we now paste the information onto the worksheet. (Ctrl + V) Right click the cell and select paste.
The information will now be displayed and updated on your worksheet.
The update time will depend on the interval set in the DDE Manager. Right-click on the minimized DDE Manager icon and select Update Interval…
We can also set individual point update times in the DDE link item. The default update time is set via the DDE Manager but we can also set the time in the individual points on the spreadsheet.
DDE Update Default Link: =CDMDDE|’C:\ACC DDE.cdm’!’\CP1L D0′
5 Second Update Link: =CDMDDE|’C:\ACC DDE.cdm’!’\CP1L D0,5′
In the Project Editor of the DDE Manager you can see the first 10 memory areas are being used. This is the yellow triangle with the lightning bolt symbol. (You will not be able to delete the point if it is in use.)
Calling up an excel file with the links embedded, will give you a Security Alert – Links warning. Select ‘Enable the content’ and then hit OK.
Here is an example of the finished excel file. We have 10 memory locations from each PLC listed. We have inserted a graph that will dynamically change when the values are read. Download the excel file here.
As you can see implementing the CX Server DDE Manager is not a difficult task. It provide a quick and efficient way to view the information that we need.
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.
In Part 1, we used VB6 to communicate from the computer to the PLC. We will now use Visual Basic for Applications (VBA) to accomplish the same task. NETComm will be the serial driver and Excel will be the program that we will use. Using Excel we will have access to the Excel Object Model so we can utilize worksheets, ranges etc.
Call up a dos prompt with administrator authority. (Right click on the cmd.exe program and select run as administrator.)
Type ‘regsvr32 netcomm.ocx’
An information box will be shown indicating that the NETComm.ocx was registered successfully.
Now open Excel and make the following on Sheet 1.
Select Developer and then Visual Basic.
If you do not have the Developer option to select, then do the following:
Select File : Options: Customized Ribbon Select Developer and hit OK
VBA – Visual Basic for Applications will open
Insert a user form.
Add NETComm1 to UserForm1. If it is not on your Toolbar, then select additional controls and select NETCommOCX.NETComm. Press the OK. Then drag this control onto your form.
Create three command buttons. This can be done by going to Design Mode, and under the Insert menu you can select Command Buttons.
Private Sub CommandButton1_Click()
If NumWords = "" Then
MsgBox "Set Read String"
Exit Sub
End If
If startcycle = 0 Then
startcycle = 1
CommandButton1.BackColor = "&H0000FF00"
Else
startcycle = 0
CommandButton1.BackColor = "&H8000000F"
UserForm1.NETComm1.PortOpen = False ' Close Communication Port
Exit Sub
End If
UserForm1.NETComm1.PortOpen = True ' Open Communication Port
Application.EnableEvents = True
Do
T$ = TRead$ ' Reset the Transmitted Information
charreturn = 11 + (NumWords * 4) ' Determine the return characters
GoSub FCS ' Checksum
GoSub communicate ' Get informaiton
'Check returned information and Display
If Mid(rxd$, 6, 2) = "00" And (Len(rxd$)) >= charreturn Then
For x = 1 To Sheets("Sheet1").Range("D7")
Sheets("Sheet1").Range("B" & x + 10 - 1) = Mid(rxd$, x * 4 + 4, 4)
Next 'x
End If
DoEvents ' Do other tasks
'Update the date and time
Sheets("Sheet1").Range("C09") = Format(Date, "YYYY/MM/DD") + " " + Format(Time, "HH:MM:SS")
Loop While startcycle = 1
If startcycle = 0 Then Exit Sub
communicate:
rxd$ = ""
Buffer = T$ + FCS$ + "*" + Chr$(13)
UserForm1.NETComm1.Output = Buffer
Time1 = Now
Timeout = Now + TimeValue("0:00:02")
Do
If Timeout <= Time1 Then GoTo timeoutcom
DoEvents
Time1 = Now()
Loop Until UserForm1.NETComm1.InBufferCount >= charreturn
rxd$ = UserForm1.NETComm1.InputData
fcs_rxd$ = Left((Right(rxd$, 4)), 2)
If Left(rxd$, 1) = "@" Then
T$ = Mid(rxd$, 1, (Len(rxd$) - 4))
ElseIf Mid(rxd$, 2, 1) = "@" Then
T$ = Mid(rxd$, 2, (Len(rxd$) - 5))
rxd$ = Mid(rxd$, 2, (Len(rxd$) - 1))
End If
GoSub FCS
If FCS <> fcs_rxd$ Then
rxd$ = ""
End If
clearbuffer$ = UserForm1.NETComm1.InputData
Return
FCS:
L = Len(T$)
A = 0
For J = 1 To L
TJ$ = Mid$(T$, J, 1)
A = Asc(TJ$) Xor A
Next J
FCS$ = Hex$(A)
If Len(FCS$) = 1 Then FCS$ = "0" + FCS$
Return
timeoutcom:
If startcycle = 0 Then Exit Sub
clearbuffer$ = UserForm1.NETComm1.InputData
rxd$ = ""
Return
End Sub
Private Sub CommandButton2_Click()
If startcycle = 0 Then
UserForm1.NETComm1.CommPort = Sheets("Sheet1").Range("A4")
UserForm1.NETComm1.Settings = Sheets("Sheet1").Range("B4") & "," & Sheets("Sheet1").Range("C4") & "," & Sheets("Sheet1").Range("D4") & "," & Sheets("Sheet1").Range("E4")
MsgBox UserForm1.NETComm1.Settings
Else
MsgBox "Stop Reading Parameters to Set MSComm"
End If
End Sub
Private Sub CommandButton3_Click()
If startcycle = 0 Then
Unit = Sheets("Sheet1").Range("A7")
If Len(Unit) < 2 Then Unit = "0" & Unit
StartADD = Sheets("Sheet1").Range("C7")
Do
If Len(StartADD) < 4 Then
StartADD = "0" & StartADD
End If
Loop Until Len(StartADD) = 4
NumWords = Sheets("Sheet1").Range("D7")
Do
If Len(NumWords) < 4 Then
NumWords = "0" & NumWords
End If
Loop Until Len(NumWords) = 4
T$ = "@" & Unit & "RD" & StartADD & NumWords
TRead$ = T$
MsgBox T$
For x = 1 To Sheets("Sheet1").Range("D7")
Sheets("Sheet1").Range("A" & x + 10 - 1) = "DM " & Sheets("Sheet1").Range("C7") + x - 1
Sheets("Sheet1").Range("B" & x + 10 - 1) = ""
Next 'x
For x = Sheets("Sheet1").Range("D7") To 200
Sheets("Sheet1").Range("A" & x + 10) = ""
Sheets("Sheet1").Range("B" & x + 10) = ""
Next 'x
Else
MsgBox "Stop Reading Parameters to Set Read String"
End If
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
End Sub
Note: The Chart on Sheet1 is just a selection of the first ten DM areas and insert a bar graph.
Running the program produces the following information:
When you open the file it will warn you about macros. This is the VBA application. Press ‘Enable Macros’.
When changing the parameters on the screen, you will also get a warning about Active X. This is the NETComm.ocx which was registered above. Press ‘OK’ to run the application.
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.
Hostlink communication protocol is a method developed by Omron for communication to PLC’s and other equipment. This ASCII based protocol is used over RS232 or RS422/RS485. It is a many to one implementation which means that you can communicate with up to 32 devices back to a master. (1:N) This communication on the industrial floor can control PLC’s, Temperature Controllers, Panel Meters, etc.
Our look at this protocol will include the wiring, setting of RS232 port settings, protocol format and writing a VB6 program to read information from the PLC. I will also point you links to then store this information into a database and share over an intranet/internet. Lets get started.
Wiring of the communication ports will depend on the equipment purchased. If communicating over 15 meters, it is recommended to switch to RS422 or RS485 connection. However I have seen RS232 runs of 50 meters without an issue. It will depend on your implementation and electrical noise in the plant.
The above diagram is the basic communication needed for RS232C. Note that the shield of the communication wire is connected only to one side. This ensures that any noise induced in the communication is filtered to one end.
Settings for RS232C communications are set in a number of ways. Older Omron C**K PLC were set through a series of dip switches. Current Omron SMR1/CPM1 PLC’s are set though data memory locations.
Note: Most of the time, you need to cycle the power or switch to program / run mode for the setting to be activated.
I generally tend to leave everything at the default settings: 9600 bps, Even parity, 7 data bits, 1 stop bit. The default host link unit number is 00. (32 max. – 00 – 31)
Protocol Format
Each piece of equipment will have a list of parameters that can be read and written using the HostLink protocol. This can be found in the programming manual of the device. Here are the areas in the CPM1/CPM1A/CPM2A/CPM2C/SRM1(-V2) from the programming manual.
Lets take a look at the command to read the DM area. All of the commands and responses will be in an ASCII format.
The command format begins with a ‘@‘ sign followed by the Node / Unit number that you wish to communicate. Header code is the command in which you with to execute. (RD) This header code will determine the next series of information. In our case the next four digits will be the beginning word followed by the next four digits to indicate the number of words. The next part of the command is the FCS (checksum) calculation. The comparison to this at each end will ensure that the command/response is correct. FCS is a 8 bit data converted into two ASCII characters. The 8 bits are a result of an Exclusive OR performed on the data from the beginning to the end of the text in the frame. In our case this would be performed on the following:
"@00RD00000010"
The last part of the command is the terminator. This is an ‘*’ followed by the character for the carriage return. (CHR$(13))
The response format begins with a ‘@’ sign followed by the Node / Unit number that you are communicating to. The header code is next (RD) followed by the End Code. The end code is a two digit ASCII code that indicates the message response / errors when executing the action. A normal code of ’00’ indicates that everything is fine. See the operation manual for the entire list of end codes for your equipment. The next part of the response depends on the header code executed. In our case it would contain the data requested. The last two parts of the response is the FCS and terminator just like the command format.
The above shows the timing of the command and responses.
Visual Basic VB6 (Example)
Now lets look at an example of reading the first 10 words from the DM area of an Omron PLC.
The first step is the design the form. You can see that we have our ten DM area words set out to populate with values. We also have a T$ for transmit. This will show what we are sending to the PLC. The RXD$ will show what the response will be from the PLC.
The MSComm is used to communicate through the serial ports of the computer. The following is the settings for the communication port.
Here is the VB6 code for the program:
When the form loads the Date/Time will get updated and Timer1 is enabled. This timer controls the interval in which the commands get executed. (Set to 1 second)
Private Sub Form_Load()
Label2.Caption = Format(Date, "YYYY/MM/DD") + " " + Format(Time, "HH:MM:SS")
Timer1.Enabled = True
End Sub
The following code will open the communication port, set the command format, send the command through the port, receive the response through the port and display the information. It will then close the communication port.
The following is the subroutine to communicate. Timer2 is the amount of time to wait before expecting an answer on the communication port. Once the command has been sent a maximum of two seconds is waited for an response. If no response nothing is returned. When the response is obtained, the FCS is checked and if correct the information is returned.
communicate:
rxd$ = ""
Buffer = T$ + FCS$ + "*" + Chr$(13)
MSComm1.Output = Buffer
Timer2.Enabled = True
Do
DoEvents
Loop Until Timer2.Enabled = False
If Time > #11:59:50 PM# Then
timeout = #12:00:02 AM#
Else
timeout = DateAdd("s", 2, Time)
End If
MSComm1.InputLen = 0
Do
If timeout <= Time Then GoTo timeoutcom
DoEvents
Loop Until MSComm1.InBufferCount >= charreturn
rxd$ = MSComm1.Input
fcs_rxd$ = Left((Right(rxd$, 4)), 2)
If Left(rxd$, 1) = "@" Then
T$ = Mid(rxd$, 1, (Len(rxd$) - 4))
ElseIf Mid(rxd$, 2, 1) = "@" Then
T$ = Mid(rxd$, 2, (Len(rxd$) - 5))
rxd$ = Mid(rxd$, 2, (Len(rxd$) - 1))
End If
GoSub FCS
If FCS <> fcs_rxd$ Then
rxd$ = ""
End If
clearbuffer$ = MSComm1.Input
Return
This is the FCS (checksum) calculation routine.
FCS:
L = Len(T$)
A = 0
For J = 1 To L
TJ$ = Mid$(T$, J, 1)
A = Asc(TJ$) Xor A
Next J
FCS$ = Hex$(A)
If Len(FCS$) = 1 Then FCS$ = "0" + FCS$
Return
This is the routine that will execute if the response is not received within the time period expected.
If you have any questions, need further information or would like a copy of this program 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.
