Connectivity Guide: TOPServer to Modicon PLC via Airlink Raven Cellular Radio Modem

Quick Links Cabling Modem Configuration TOP Server Configuration Testing TOP Server Communications Frequently Asked Questions Troubleshooting Summary

Introduction:

The following paper explains the steps that we have taken (here, at the Software Toolbox testing lab) to connect a Modicon Micro PLC to an Airlink Raven modem, for the sole purpose of allowing communications between our TOP Server Modbus Driver and the Modicon Micro via the Airlink Raven Radio.

We have also tested TOP Server connectivity to Allen-Bradley PLC/5 and SLC5/04 PLCs via the Airlink Raven modem. For this whitepaper though, we have chosen to focus on the Modbus Micro PLC as this setup appears to be the most common.

Although this paper was written around the Modicon 311 Micro PLC we have in our lab, the general concepts covered here apply to any Modicon PLC with a Modbus RTU Serial connection or for that matter, any Modbus RTU device with a Modbus RTU serial connection.

Who this paper is for:

The following paper is designed for the engineers who handle the PLC and Airlink hardware directly.

Software and Hardware discussed:

In this paper, we largely concentrate on the cabling between the Airlink Raven modem and the Modicon Micro PLC.

We discuss the TOPServer OPC Server connectivity last.

Contacting Technical Support:

Depending upon the help needed will dictate which company you should contact for Technical support, whether it be Airlink or Software Toolbox:

• Modem issues: Airlink
• Cabling issues: Airlink or Software Toolbox, Airlink being the primary.
• Connectivity - Modem configuration: Airlink
• Connectivity - TOPServer configuration: Software Toolbox
• Debugging: Airlink and Software Toolbox

Contact details are:

Airlink Software Toolbox Web: http://www.airlink.com/support/ Email: support@airlink.com Tel: 510-264-5400 Web: http://support.softwaretoolbox.com Email: support@softwaretoolbox.com Tel: 704 849-2773 Fax: 704 849-6388

Cabling:

If you have a cable that will work from a PC com port to talk to the PLC/Modbus Device, then you can make that cable work with the Airlink Raven most likely by simply adding a null modem adapter and any gender changers needed to the PC end of that cable before you connect it the Airlink.

The following is a cable diagram of the cable we (Software Toolbox) created in our Lab to connect to our Modicon Micro PLC, which uses an RJ45 connector. The Airlink Raven uses a DB-9 Connector.

The following diagram shows the single cable with the DB-9 connection to the left, and the RJ45 connector to the right:

You will notice that PIN #4 on the DB-9 connector has 2 wires:

• · one going to PIN #6 on the RJ45 connector
• · one looping to PIN #6 on the same DB-9 connector (jumpered)

Step 1 - Testing this cable

• Once this cable is prepared, you should use it to connect your PC to the PLC/Device directly! This is an important step in both getting communications to work, and is a valuable piece of information to have available if problems arise when introducing the Airlink Raven modem into the equation.
• You should use the PLC Programming Software to test the communications.
  If you do not have the programming software, then you could try the TOPServer Modbus Serial driver running in Serial mode (i.e. not using Ethernet Encapsulation) and then launching the OPC quick client.

Step 2 - Using this cable to connect Airlink Raven to Modicon Micro

• Using this cable alone will not work!
• You will need a regular NULL MODEM ADAPTER which you will plug into the Airlink Raven modem:

Airlink Raven Modem > Null Modem Adapter > Cable > Modicon Micro PLC/Device

Modem Configuration:

The following is our Airlink Raven modem configuration. Below you will find the COMPLETE listing of ALL of the values within our Modem. Your settings will differ. Extract from this configuration the COM port configuration settings.

It is IMPERATIVE that you have the Baud rate, Parity, and Stop Bit settings on the modem's COM port set to MATCH those on your PLC.

Questions relating to your Modem configuration should be directed to Airlink directly.

Click anywhere in this sentence to show/hide our Airlink Raven Modem Settings:

Foreword

If you are new to the TOPServer and don't know where to start, then try one of our TOPServer Quick Start Guides. We have:
 

• Streaming Video Presentation
• Microsoft Word Document
   

If you have not installed the TOPServer, then you can download it from here: download TOPServer

During the installation you can specify which driver(s) to install, or install everything. You should at least specify the "Modbus Serial" protocol by minimum (we recommended selecting the "Modbus Suite" option)

Our TOPServer configuration is shown below as screenshots:

Channel Properties:

This is the ONLY Tab for which we set any properties, and that would be to use Ethernet Encapsulation. All other tabs were left with DEFAULT values.

Device Properties:

In the above screen, we have specified the Modbus Device Address (ID) of the device.
It is imperative that this setting is correct. You will need to ask the person who setup your PLC what its Device Address (ID) is if you do not know. You can usually figure this out using the PLC programming software. You can always try "1" to see as many Modicon PLCs and Modbus Devices default to a Device Address (ID) of 1, but if it's not that then you'll have to find out. There is no way for Airlink or Software Toolbox to "guess" what your Device Address (ID) of your PLC or Modbus Device is.

In the above screen, we have defined the IP Address of our Airlink Raven modem (our Raven uses a static IP). Some of your Airlink Raven modems may have dynamic IP Addresses, if so then you will need to enter the most current IP address in this window. When the IP Address changes, you will need our OPC Server Manager software to intercept those changes and update the TOPServer configuration accordingly. This subject is not in the scope of this specific paper, but please do visit the OPC Server Manager website for more information and a download of the product.

We have also specified the DPORT (Data Port) address that the Airlink Raven is listening on. We have also specified that we are using TCP/IP as our transport. The DPORT setting is found in the Airlink Raven configuration, see the Modem example listing above.

It is absolutely crucial that ALL of the settings in this screen are correct.

You can see from the above screen that we have INCREASED our timeout settings vs. the default settings. This is because the initial connection between the TOPServer and the Airlink Raven may take some time. Secondly, we have also increased the REQUEST TIMEOUT property to 2-seconds so as to compensate for the additional delays incurred by communicating to this modem via the internet. Your settings "may" need to be increased further.

Download our TOPServer Configuration file (*.OPF): TOPServer-MicroAndRaven.opf

NOTE: if you wish to download our TOPServer configuration to try and communicate to our Modicon Micro 311 PLC via our Airlink Raven modem, then please do call us (Software Toolbox technical support) in advance so that we can make sure the hardware is powered-up and available.

Tel: (704) 849-2773

Testing the TOPServer Communications:

The key in troubleshooting this kind of equipment setup is understanding what and how to troubleshoot, and the tools that are available to you.

Going back to the testing the cabling section we mentioned that you should test the cable between the PC and PLC/Device before introducing the Airlink Raven. By doing this, we can assure that the cabling is ok, the COM port on the PLC/Device is ok and that general communications is good.

Once the Airlink Raven has been introduced into the equation, then the tools that are available in the TOPServer will be the only form of diagnostics available, unless you have some kind of packet -sniffing abilities, or if Airlink provides some diagnostics abilities within the modem (a feature which does not exist as of March 10, 2004 - but is expected in a future firmware versions of the Ravens).

TOPServer Diagnostics:

The TOPServer diagnostics window is accessed by right-clicking on the Channel (ours is called "modbus") and choosing the "Diagnostics" option from the menu.

NOTE: if this option is not present in the menu, then open the Channel Properties instead, and then enable the checkbox called "Enable Diagnostics" which is found in the "General" tab.

Once the diagnostics screen is open, you will see a black area of the screen. This area shows the protocol that is being sent and received. Under this area, are some statistics showing the number of successful/failed reads and writes.

You MUST have a client connected to the TOPServer and at least
reading a Tag for this screen to be of any use. A Client in this case
may be our OPC Quick Client (supplied with the TOPServer)
or your HMI/Scada package.

A screenshot is shown below:

Frequently Asked Questions:

Question: When does this data show-up in the Diagnostics Window ?
Answer : As Ethernet Encapsulation is being used, a connection (socket-connection) must be established with the Airlink Raven before any other communications (intended for the PLC/Device) can occur. Therefore, once a socket-connection to the Raven has been established, you will see the packets we (TOPServer) are sending also appear in this screen.
No socket-connection to the Raven will result in no data being shown here.
Recommendation: Verify the Airlink Raven:

• Is the radio in fact online
• IP Address is correct
• Port is correct
• You may wish to try and power-cycle the Raven modem.

Question: What if I see only GREEN (Tx) data?
Answer: This means that a socket-connection to the Raven has been established, meaning that your communications configuration is correct in the TOPServer.
However, it is most likely that the configuration in the Airlink Raven is not correct for communicating to the Modicon.
Recommendation: Verify the COM port settings in the Airlink Raven.

Question: What if I see no indication of anything happening, not even a failed read?
Answer: Verify that you have client attached to the TOPServer, it must be actively reading (subscribing) to a tag by minimum.
Recommendation: Launch the OPC Quick Client from the TOPServer toolbar.

Recommended Debugging Steps:

The following list is merely a guideline as to how we recommend you approach your debugging. By following these steps and documenting your findings, when contacting either Airlink or Software Toolbox and having this data already available will result in a much faster turn-around in identifying the problem and solving it.

• Test the PLC/Device connectivity by connecting it DIRECTLY to the PC at first and using your PLC Programming Software (if possible).
• Test the TOPServer connectivity to the PLC/Device with the PLC/Device connected to the PC directly.
• Change your hardware setup to use the Airlink Raven modem by disconnecting the PLC/Device from the PC, and connecting the PLC/Device to the Airlink Raven instead.
• Test the connection between the TOPServer and the Airlink (using the information in the TOPServer Diagnostics section as a guideline) and verify that a socket-connection is taking -place. You will know when a socket is connected because you will Transmit (Tx) data being sent.
• Disconnect the OPC Quick Client from the TOPServer, verify that NO clients are connected to the TOPServer and then:
• Power-cycle the Airlink Raven
• Power-cycle the Modicon PLC/Device
• Restart/Re-connect the OPC Quick Client to the TOPServer.
• Open the TOPServer diagnostics window and view the tag values in the OPC Quick Client

Summary:

This paper has explained the following:

• · Serial RS232 Cable pin-out for a Modicon Micro PLC
• · Using a Null Modem Adapter to connect the above-mentioned Cable to an Airlink Raven modem
• · Configuring the Modem/PLC
• · Configuring the TOPServer to communicate to the Modicon Micro PLC via the Airlink Raven modem
• · Troubleshooting

If you have any questions or comments regarding this sheet, then please let us know by emailing: tech@softwaretoolbox.com

If you require Technical Support, please be sure to contact the correct party using the guidelines outlined in the above Contacting Technical Support section.