Programming a PLC through VB

Hi everyone,

I am wondering how to communicate to a PLC using VB. I currently have a "Click PLC programming module", that I am communicating to through an RJ12-USB converter. I have a sample VB program that allows me to connect to the device serially, but I am unsure how to go about actually programming code to communicate to the PLC.

I have seen examples that showcase assembly language code to speak to PLCs, but I have no idea where to begin with this particular PLC. How does one figure out the assembly level language code associated with a PLC?

My goal: To read inputs (via pushbutton) into the PLC, and then send an output signal over an ethernet server. I have a background in PLCs, and in VB, but am not sure how to bring both of these systems together.

I thank you all in advance, and appreciate your support.

Hassman said:

How does one figure out the assembly level language code associated with a PLC?

Click to expand...

By getting an engineering job with a company that designs and manufactures those PLCs. This is a closed information owned by the manufacturer.

Now, many PLC brads do publish a communication protocol that allows to read and modify the data inside the PLC memory. But no one ever publishes any method to read and modify the code.

Hassman said:

My goal: To read inputs (via pushbutton) into the PLC, and then send an output signal over an ethernet server. I have a background in PLCs, and in VB, but am not sure how to bring both of these systems together.

Click to expand...

We've done one project using a Wago PLC (Codesys based programming) that talks to a computer through a Telnet connection.

Using a standard Windows command prompt one can enter commands that the PLC interprets and executes. Looking at the first Google result (http://www.teachexcel.com/excel-help/excel-how-to.php?i=433987) one can create Telnet connections using Excel.

Another option would be add a Modbus/TCP stack on the computer. I'm pretty sure there's some free things floating around for Linux for that. Windows should have something as well.

Use the Modbus protocol to request the state of inputs. Also use it to set internal states which would be used by a simple program within the Click PLC to direct the state of outputs.

The internal PLC program should monitor the state of communications from the controlling PC program and place the outputs into a safe state - usually off - if the communication fails.

Not VB related but I would recommend going to the webpage in the link below. There is a large amount of info there including free software, manuals, and Technical Info.
Link:
http://www.automationdirect.com/adc...ware/CLICK_PLC_Programming_Software?learnsite

keshik said:

We've done one project using a Wago PLC (Codesys based programming) that talks to a computer through a Telnet connection.

Click to expand...

Depending on the required connection speed you could go several routes with the Wago - SQL, HTTP, File swapping, and of course ModbusTCP. I agree with keshik and others who recommend ModbusTCP because of its simplicity and and availability. If you're using any CoDeSys PLC (correct me if I'm wrong) there is a CoDeSys OPC server which is free (again, correct me if I'm wrong.) I've never used it but my son has and he says that it works well.

Good luck,

Yosi

Wonderful advice everyone and thank you for the links.

I believe Modbus is the best route to go, at least for what I need to get done right now. I will report back in the next couple of days, and hopefully shed some light as to my progress.

Thank you all again....great support as always

OP, it looks like we went down a totally tangent road. You're using an Automation Direct PLC with two RS-232 ports by default and a USB adapter. Nothing that Modbus/TCP or Codesys has any real relevance with.

Take a look at chapter 4 in the manual: http://www.automationdirect.com/static/manuals/c0userm/c0userm.pdf I think the ASCII section might be useful.


Try looking at this: http://dev.emcelettronica.com/serial-port-communication-excel-vba

Hi Keshik,

Ok now I'm a little confused. When I called automation direct and spoke to the representatives they said that the click was based on the Modbus protocol, but now you're saying that it's not compatible.

Can you help clarify this for me Keshik??

keshik said:

You're using an Automation Direct PLC with two RS-232 ports by default and a USB adapter.

Click to expand...

They are Modbus by default, your device (PC) would be serial/USB to the CLICK then Ethernet out to what ever you are doing after

Hassman, It may help if you give a little better detail of your project

Hassman said:

Hi Keshik,

Ok now I'm a little confused. When I called automation direct and spoke to the representatives they said that the click was based on the Modbus protocol, but now you're saying that it's not compatible.

Can you help clarify this for me Keshik??

Click to expand...

Yup, I hope I can. There are two main flavors of Modbus. One is Modbus/RTU which runs over RS-232/422/485 and is serial. The other is Modbus/TCP with runs over Ethernet. I, and I think most of the above posters, were referring to Modbus/TCP which is the Ethernet format and the Click doesn't support as far as I can tell.

So that leaves us with using serial communications with the Click (so no Modbus/TCP). That should let you use either ASCII or Modbus/RTU to your computer. I'm guessing that to integrate with Excel ASCII will probably be simpler but I could be wrong. I haven't done what you're doing before.

keshik in Hassman first post... "I am communicating to through an RJ12-USB converter"

To me, he is going USB (modbus) then out of the PC to something else (reporting ?) via Ethernet (not RTU)

geniusintraining said:

keshik in Hassman first post... "I am communicating to through an RJ12-USB converter"

To me, he is going USB (modbus) then out of the PC to something else (reporting ?) via Ethernet (not RTU)

Click to expand...

My impression was:
PC <--> USB/Serial Converter <--> Click PLC

I'm not sure that I'm correct anymore, however. I think the OP might need to clarify this. I now see the reference to an Ethernet server. The Click doesn't have Ethernet so we're going to need something in the middle.

OP, can you list what you're exactly trying to communicate from/to/with?

Hi guys,

First off, thank you Keshik, I did notice that the above posters were talking about the Modbus tcp/ip but I am aware that the click does not support that and was intending on communicating via Modbus/RTU

Secondly, to follow up on GeniusInTraining's post:

There is a small production line with operators. The goal is to develop a system with 6 inputs (pushbutton), and 6 respective outputs.

When one of these inputs is triggered (low to high) then it will send a signal to its corresponding output, with an error code. That error code will be sent to the local web server, and logged into the web servers database.

Basically there are 6 possible errors in the production line, and whenever an operator notices one of these errors, then they will press the corresponding pushbutton, and we need to log these errors into the database (all of this in real-time).

I hope that clarifies it.

Thirdly in regards to communication, Keshik you are correct, with one addition:

Ethernet<--> PC <--> USB/Serial Converter <--> Click PLC

So the setup is to take the Click PLCs input (pushbuttons), then to take that input signal, prepare an error code through the VB C#, and then transmit it through Ethernet to a web server.

Am I correct in presuming that I can do this, or am I missing something? Thank you all for your patience and support.

Regards,

Hassan

Thanks for the additional information. That all seems doable. You'll probably want some sort of method for the PC to have a heartbeat with the PLC to make sure they can talk (and you can then log that as an error). As long as the heartbeat is good you could probably just have the Click send an ASCII string on-demand whenever a button is pressed. Shouldn't be horribly complicated.